Scalable motion control system

ABSTRACT

A control system includes a clustered architecture having a master controller, a central control section including one or more first remote controllers under direct control of the master controller, and a distributed control section including a cluster controller controlled by the master controller. The cluster controller controls the activities of one or more second remote controllers. Each of the first and second remote controllers are utilized to drive one or more axes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.13/011,970, filed 24 Jan. 2011 (now U.S. Pat. No. 9,020,617), which is adivisional of U.S. patent application Ser. No. 11/178,615, filed 11 Jul.2005 (now U.S. Pat. No. 7,904,182), which claims the benefit of U.S.Provisional Application No. 60/688,636, filed 8 Jun. 2005 all of whichare incorporated by reference herein in their entirety.

The disclosed embodiments are related to a control system for complexmulti-axis non-linear machines, in particular, to a system for accurateand synchronized control of precision robots with a desirablecombination of performance, flexibility, and scalability.

BACKGROUND

As a result of technological improvements in the area of electronics andcommunication, control technology for complex motion systems has taken aclear direction toward a networked architecture. A networked solutionutilizes multiple simple controllers, referred to as remote controllers,which are located close to the components subject to control, such asmotors and other actuators, and are coordinated by a master controllerthrough a communication network.

The networked architecture opens numerous challenges in the areas of thedivision of the controls intelligence between the master and remotecontrollers, implementation of advanced control algorithms,communication network utilization, synchronization of components drivenby different remote controllers, handling of events associated withinputs on multiple remote controllers, such as capturing positions ofmultiple axes of motion, accommodating a human presence in the workspace, and dealing with power loss situations.

The division of the controls intelligence between the master and remotecontrollers may vary from a fully centralized architecture, where all ora majority of the control algorithms run on the master controller, to adistributed solution, where control algorithms are implemented onsubstantially autonomous remote controllers.

The benefits of a highly centralized architecture include the ability toprovide advanced control algorithms, which often require real-timeinformation from multiple axes, such as multi-input-multi-output (MIMO)control, and can be conveniently implemented on the master controller.The remote controllers in such an architecture require comparatively lowcomputational power and small amounts of on-board memory, allowing for arelatively simple and inexpensive design.

These advantages may be achieved at the cost of a relatively highutilization of the communication network due to intensive time-criticaldata exchange between the remote controllers and the master controllerbecause the master controller is closing the control loops. Thesesystems usually have limited scalability because the maximum number ofaxes is constrained by the computational power of the master controlleras well as the bandwidth of the communication network. In addition,since the remote controllers may not have enough intelligence toautonomously support failure-related operations, such as performing acontrolled stop of the respective motion axes in the case of a failureof the communication network, satisfactory control in the event of afailure may be problematic to achieve.

In contrast, control systems with distributed control algorithms, whichclose the control loops on the remote controllers, executing ontrajectory information received from the master controller, utilizecomparatively low network traffic and substantially less time-criticaldata that may be conveniently buffered at the remote controllers toimprove the overall capacity margin of the communication network. Thisapproach may provide desirable scalability of the control system sinceincreasing the number of remote controllers for additional axesautomatically increases the overall computational power available forexecution of the control loops. Furthermore, the remote controllers,being capable of generating simple trajectories and running controlalgorithms, have enough intelligence to support failure-relatedoperations, such as a controlled stop, in the case of a failure of thecommunication network.

However, the additional intelligence of the remote controllers in thedistributed architecture requires more computational power and memory,which generally makes the remote controllers more expensive. Also,implementation of full MIMO control algorithms is problematic since thecontrol algorithms running on one remote controller generally do nothave real-time access to the states of the axes driven by other remotecontrollers.

Implementation of a networked control system is generally facilitated byusing a communication network with the appropriate capabilities. TheIEEE 1394 communication network, also known as FireWire, is based on ahigh-speed serial bus which was developed to provide the same servicesas modern parallel buses, but at a substantially lower cost. The IEEE1394b-2002 amendment defines features and mechanisms that providegigabit speed extensions in a backwards compatible fashion and detectionof physical loops in the bus topology and their subsequent resolution byselective disabling of physical layer (PHY) ports. A lightweight IEEE1394 protocol was developed for efficient asynchronous communication toelectronic instrumentation and industrial control devices by the 1394Trade Association. Referred to as the Instrument and Industrial ControlProtocol (IICP), it uses a dual-duplex plug structure for transfer ofdata and command/control sequences in a flow-controlled manner.

Control systems for accurate and synchronized control of precisionrobots generally require a certain level of system integrity, that is,the control systems may require interlocks, fail safe mechanisms,mechanisms for maintaining a minimum 100% up time, mechanisms andtechniques to avoid damage to products being produced, and mechanismsand techniques to accommodate a human presence in workspaces of thecontrol system.

State-of-the-art electronics and computers that implement programmablesystems with a specified level of integrity tend to be marketed to thehigh-end of industrial machinery and processes. These types of systemsare generally applicable to more stringent categories, for example,EN954 Category 4 or IEC61508 SIL 3, and use high-end processors orembedded CPU's. These types of systems are generally expensive and havemore capability than required for low-end machinery or systems requiringlower levels of integrity, such as Category 2 or 3.

A machine designer who wishes to implement an alternative solution toprogrammable integrity to avoid the added cost of the specializedhigh-end electronics is faced with an extremely complex task of makingthe electronics, network and software of a control system meet integrityrequirements and obtaining regulatory authority or auditor approval.Another issue with the existing technology that implements a specifiedlevel of integrity is size and form-factors, which are unsuitable forintegrity applications with stringent space constraints.

There is a need for a control system that has the advantages of both acentralized and distributed architecture, that is flexible and scalable,that synchronizes component operations, that accommodates power lossesand human presence in a workspace of the components subject to control,and that provides required system integrity levels.

SUMMARY

The disclosed embodiments are directed to a control system including aclustered architecture having a master controller, a central controlsection including one or more first remote controllers under directcontrol of the master controller and a distributed control sectionincluding a cluster controller controlled by the master controller,wherein the cluster controller controls the activities of one or moresecond remote controllers. Each of the first and second remotecontrollers are utilized to drive one or more axes.

The disclosed embodiments are also directed to a method of operating anaxis of a control system that includes generating a trajectory for theaxis in terms of a position, velocity, and acceleration for each pointof a plurality of points on the trajectory, and calculating an inversedynamic model of the axis to determine a gain value and a feedforwardterm for each point.

The disclosed embodiments are further directed to a method ofsynchronizing nodes on a network, including issuing a start messageincluding a time stamp indicating the time the message was sent,updating a high resolution clock using the time stamp, and compensatingfor a difference between a time indicated by the time stamp and a timethe high resolution clock was updated.

The disclosed embodiments are still further directed to a message setfor communicating among nodes of a control system that includes anaction message for exchanging commands and command responses, an eventmessage for reporting data relating to a predetermined event to a mastercontroller, a string message for providing a serial message channelbetween a remote controller and the master controller, and a data portmessage for sending data to a network node.

The disclosed embodiments also include a method of obtaining axis dataat the time of an event, including buffering data at one or more axisnodes, recording time information of a triggering event occurring at atriggering event node of the one or more axis nodes, and processing thebuffered data to determine a set of values at a time period indicated bythe recorded time information.

The disclosed embodiments are yet further directed to a control systemhaving a plurality of nodes organized in a clustered architecture, and awireless communication network through which two or more of the nodescommunicate.

The disclosed embodiments also include a method for controlling an axisof a control system including calculating an operating parameter valuefor an end effector of the axis, and generating a motion profile for anindividual joint of the axis such that a motion profile for the endeffector does not exceed the operating parameter value.

A method for controlling an axis is also disclosed that includescalculating a velocity and a torque for a position of the axis,predetermining a first maximum time period during which an axis velocitymay exceed the calculated velocity, predetermining a second maximum timeperiod during which an axis torque may exceed the calculated torque, anddisabling the axis if the first or second maximum time period isexceeded.

Another embodiment disclosed herein includes a method of verifying theintegrity of data transmitted over a control system network. The methodincludes storing operating parameters at a node on the network, andverifying that commands received through the network do not causeoperations of the node that exceed the operating parameters.

A method of verifying the integrity of a control system network as partof the disclosed embodiments includes issuing a periodic message, anddisabling one or more nodes of the control system network if the messageis not received within a time period.

The disclosed embodiments also include a method of maintaining theintegrity of a control system network including assigning nodes of thenetwork into zones such that motion in a first zone is isolated frommotion in zones other than the first zone, and controlling the zones sothat events of the first zone do not effect the operation of zones otherthan the first zone.

The present embodiments are also directed to a method of bringing anaxis to a controlled stop, that includes determining if power has beenlost to a system including the axis, applying a trajectory to the axisthat brings the axis to a zero velocity within a predetermined timeperiod, and removing power from the axis at the end of the predeterminedtime period.

The embodiments described herein also include a method for compensatingfor synchronization delays in a control system that include determininga delay between a network node issuing a message and a network nodereceiving the message, and using the determined delay to adjusttrajectory data for the receiving node.

A method of operating a robot is disclosed that includes recording anidle time of the robot, determining performance characteristics of therobot upon exceeding an idle time threshold, and directing the robot toperform a warm up exercise if the determined performance characteristicsdo not meet a specification.

An application program interface for a motion control system is alsoincluded in the disclosed embodiments and includes a standardized set ofinterface conventions for exchanging information among components of themotion control system, and a generalized command set that providesgeneral commands to perform operations and specific arguments toidentify particular components and actions for performing theoperations.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other features of the disclosed embodimentsare explained in the following description, taken in connection with theaccompanying drawings, wherein:

FIGS. 1(1 a-1 b) shows a block diagram of a clustered architecturecontrol system suitable for practicing the disclosed embodiments;

FIG. 2 shows a block diagram of a master controller that controls theoperation of the clustered architecture control system;

FIG. 3 depicts a block diagram of a cluster controller capable ofoperating under control of the master controller;

FIG. 4 shows a block diagram of a remote controller capable of operatingunder control of the master controller or a cluster controller;

FIG. 5 a shows an exemplary application of the clustered architecturecontrol system;

FIG. 5 b shows an exemplary application of the control system usingautonomous remote controllers;

FIG. 6 shows an exemplary PVT frame used to convey position, velocity,and time information;

FIG. 7 shows an exemplary PVT-FG frame used to convey position,velocity, and time information with feedforward and gain terms;

FIG. 8 shows a comparison of empirically derived tracking errors usingdifferent types of control algorithms;

FIG. 9 a shows an exemplary bus cycle of the communications network ofthe disclosed embodiments;

FIG. 9 b shows an exemplary cycle start message of the communicationsnetwork of the disclosed embodiments;

FIG. 9 c shows an exemplary high resolution register for synchronizationamong communication network nodes;

FIG. 10 shows a communication protocol structure;

FIG. 11 shows a plug implementation as part of the communicationsprotocol structure;

FIG. 12 shows a diagram of a work cell;

FIG. 13 shows flow diagrams for an instantaneous data capture sequence;

FIG. 14 shows flow diagrams for another embodiment of an instantaneousdata capture sequence;

FIG. 15 shows flow diagrams for still another embodiment of aninstantaneous data capture sequence;

FIG. 16 shows a flow diagram for a procedure to calibrate for signaltransition delays;

FIG. 17 shows an exemplary control message structure;

FIG. 18 shows an exemplary ACTION message;

FIG. 19 shows an exemplary EVENT message structure;

FIG. 20 shows an example of a vendor specific EVENT message;

FIG. 21 shows an example of a STRING message structure;

FIG. 22 shows an example of a vendor specific STRING message;

FIG. 23 shows an example of a PVT or PVT-FG message structure;

FIG. 24 shows an example of a STATUS message;

FIG. 25 shows a portion of the system of FIGS. 1(1 a-1 b) where acommunications network has a wireless segment;

FIG. 26 shows an exemplary PVT frame with an optional torque limit term;

FIG. 27 shows an exemplary PVT-FG frame with an optional torque limitterm;

FIG. 28 shows a block diagram of a remote controller with a commonintegrated checking and shutdown circuitry unit;

FIG. 29 shows a diagram of a work cell suitable for implementing a robotwarm up exercise;

FIG. 30 shows a flow diagram of an implementation of a robot warm upexercise procedure;

FIG. 31 shows a flow diagram of an alternative robot warm up exerciseprocedure;

FIG. 32 shows an example of a TRACE message;

FIG. 33 shows an example of a capacitive storage module;

FIG. 34 a shows an exemplary network topology that provides redundantconnections;

FIGS. 34 b-34 e show various aspects of a network failure compensationscheme;

FIG. 35 shows a method of determining and applying repeater delays;

FIG. 36 shows an exemplary PVT frame with an additional TIME_OFFSETfield;

FIG. 37 shows an exemplary PVT-FG frame with an additional TIME_OFFSETfield;

FIG. 38 shows a typical network self identification scheme;

FIGS. 39(39 a-39 c) shows an example application of a control systemwith multiple zones;

FIG. 40 shows a block diagram of power control circuitry;

FIG. 41 shows another example of power control circuitry connected to acapacitive storage module; and

FIGS. 42(42 a-42 c) shows a block diagram of an application programinterface.

DETAILED DESCRIPTION

FIGS. 1(1 a-1 b) shows a block diagram of a system 100 suitable forpracticing the embodiments disclosed herein. Although the disclosedembodiments will be described with reference to the embodiment shown inthe drawings, it should be understood that the disclosed embodiments canbe embodied in many alternate forms of embodiments. In addition, anysuitable size, shape or type of elements or materials could be used.

The control system 100 of the disclosed embodiments combines thebenefits of a centralized and a distributed allocation of controlsintelligence in a networked control system. This combinatorialarchitecture is referred to herein as a clustered architecture.

The clustered architecture control system 100 includes a mastercontroller 105, one or more cluster controllers 110, one or more remotecontrollers 115, and one or more autonomous remote controllers 150connected together through a communication network 120. The mastercontroller 105, the cluster controllers 110, the remote controllers 115and the autonomous remote controllers 150, may be referred to as networknodes.

As depicted diagrammatically in FIGS. 1(1 a-1 b), the master controller105 supervises the overall operation of the control system 100, each ofthe cluster controllers 110 supervise the operations of one or moreremote controllers 115, and each of the remote controllers are utilizedto drive one or more axes 125. The axes may be part of one or morecomplex multi-axis non-linear machines, for example, a system ofprecision robots. The remote controllers 115 may be controlled by acluster controller 110 and autonomous remote controllers 150 may beoperated directly by the master controller 105. Remote controllers 115may be generally grouped together in clusters 130.

The clustered architecture control system 100 may also include at leastone bridge node 135 which allows the master controller to communicatewith nodes on another communication network, such as a controller areanetwork (CAN). The control system may then be able to control CAN basedmodules and components, for example, CAN axis controllers, grippers,doors, actuators, sensors, etc.

The clustered architecture provides the features of a centralizedcontrol network and the features of a distributed control network whererequired, within the network topology. The architecture as disclosedherein is advantageous because clusters 130 may be distributed whererequired within the network, and each cluster controller 110 is capableof providing highly centralized control within the cluster it manages.Network traffic associated with highly centralized control is generallyconfined within each cluster 130 and remote controllers 115 andautonomous remote controllers 150 may be located close to axes theycontrol, reducing problems associated with power and signal cabling. Inaddition, the architecture allows for direct control of the autonomousremote controllers 150 by the master controller 105 where required.Furthermore, because intense network traffic is generally confinedwithin the clusters 130, and the clusters 130 are capable of a highlevel of control, the architecture may accommodate a large number ofclusters. Thus, the architecture provides a high level of scalabilityand allows for an efficient distribution of controllers.

As a centralized control example, the master controller 105 may directlycontrol an autonomous remote controller 150, where the master controllermay generate trajectories, run control algorithms and provide torquecommands for implementation by the autonomous remote controller 150. Theautonomous remote controller 150 may use the torque commands to producecontrol actions such as applying voltage to an axis actuator 140, forexample, a motor. The autonomous remote controller 150 may also readfeedback signals such as position information from a feedback device145, for example, an encoder and current draw from the axis 125 andconvey those to the master controller 105. In this example, while highperformance is achieved, network utilization may also be high becausethe control and feedback loops are closed over the communication network120.

As a distributed control example, the master controller 105 maycoordinate activities among one or more autonomous remote controllers150 and generate trajectory data for implementation by one or moreautonomous remoter controllers 150. The autonomous remote controllers150 may use the trajectory data in real time control algorithms toproduce control actions such as applying power to axis actuators 140,and may also convey status information to the master controller 105. Inthis example, network utilization may be low since the feedback controlloops are closed on the remote controllers. However, control performanceof dynamically coupled axes may be limited because the feedback controlloops generally do not have real-time access to information residing onother remote controllers.

As an example of a combinatorial clustered control, the mastercontroller 105 may perform high level supervisory control functions andcoordinate activities among one or more cluster controllers 110. Acluster controller 110 may run real time control algorithms includinglocal dynamic modeling of the axes under its control and provide torquecommands to its respective remote controllers 115. The remotecontrollers managed by the cluster controller 110 may, for example,apply power to axis actuators 140 in response to the torque commands,and may also convey axis information, such as actual positions, to thecluster controller 110. Thus, most control and feedback communicationmay generally occur locally between the cluster controller 110 and itsrespective remote controllers 115, conserving network utilization amongnodes outside of the cluster.

The clustered architecture generally provides high performance controlfor subsets of components where necessary without burdening the entirecommunication network 120 with heavy time-critical traffic.

Turning now to FIG. 2, the master controller 105 will be described ingreater detail. As mentioned above, master controller 105 controls theoperation of the clustered architecture control system 100. Mastercontroller 105 may generally include a processor 205, read only memory210, random access memory 215, program storage 220, a user interface225, and a network interface 230.

Processor 205 may include an on board cache 235 and is generallyoperable to read information and programs from a computer programproduct, for example, a computer useable medium, such as on board cache235, read only memory 210, random access memory 215, and program storage220.

Upon power up, processor 205 may begin operating programs found in readonly memory 210 and after initialization, may load instructions fromprogram storage 220 to random access memory 215 and operate undercontrol of those programs. Frequently used instructions may betemporarily stored in on board cache 235. Both read only memory 210 andrandom access memory 215 may utilize semiconductor technology or anyother appropriate materials and techniques. Program storage 220 mayinclude a diskette, a computer hard drive, a compact disk (CD), adigital versatile disk (DVD), an optical disk, a chip, a semiconductor,or any other device capable of storing programs in the form of computerreadable code.

On board cache 235, read only memory 210, random access memory 215, andprogram storage 220, either individually or in any combination mayinclude operating system programs. The operating system programs may besupplemented with an optional real time operating system to improve thequality of data provided by the master controller 105. The optional realtime operating system may also allow the master controller 105 toprovide a guaranteed response time to data and messages received fromthe cluster controllers 110 and the autonomous remote controllers 150.

In particular, on board cache 235, read only memory 210, random accessmemory 215, and program storage 220, either individually or in anycombination may include programs for axis trajectory generation, dynamicmodeling, error handling, data collection, and a messaging facility. Themessaging facility may include programs for constructing and exchangingmessages among network nodes, programs for constructing and exchangingframes, and may include programs for providing an applications programinterface, as disclosed below. In addition, on board cache 235, readonly memory 210, random access memory 215, and program storage 220 maybe loaded with new or upgraded programs, for example, by processor 205through network interface 230.

Network interface 230 may be generally adapted to provide an interfacebetween master controller 105 and communication network 120.Communication network 120 may include the Public Switched TelephoneNetwork (PSTN), the Internet, a wireless network, a wired network, aLocal Area Network (LAN), a Wide Area Network (WAN), a virtual privatenetwork (VPN) etc., and may further include other types of networksincluding X.25, TCP/IP, ATM, etc. In one embodiment, communicationnetwork 120 may be an IEEE 1349 network, also referred to as a“Firewire” network.

Master controller 105 may include a user interface 225 with a display240 and an input device such as a keyboard 255 or mouse 245. The userinterface may be operated by a user interface controller 250 undercontrol of processor 205. The user interface controller may also providea connection or interface 255 to an external network, another controlsystem, or a host computer.

The master controller 105 may generally perform high-level supervisoryand control functions for the clustered architecture control system 100.These functions may include providing a communication interface with anoperator and/or a higher level host computer, configuration datamanagement, coordination of the cluster and remote controllers, motionsequencing and trajectory generation, dynamic modeling (if required),error handling and data logging.

Turning now to FIG. 3, the structure and operation of a clustercontroller 110 will be described. While a single cluster controller 110will be described, it should be understood that the clusteredarchitecture control system 100 may include any number of clustercontrollers.

As previously mentioned, cluster controller 110 may receive informationfrom master controller 105 and may utilize that information to controlone or more axes 125. Cluster controller 110 may generally include aprocessor 305, read only memory 310, random access memory 315, programstorage 320, and a network interface 330 to communication network 120.Processor 305 may also include an on board programmable memory 335.

Processor 305 is generally operable to read information and programsfrom a computer program product, for example, a computer useable medium,such as on board programmable memory 335, read only memory 310, randomaccess memory 315, and program storage 320.

On board programmable memory 335, read only memory 310, random accessmemory 315, and program storage 320 may include programs forconstructing and exchanging messages among network nodes and may includeprograms that support an applications program interface among networknodes. On board programmable memory 335, read only memory 310, randomaccess memory 315, and program storage 320 may also include programsthat allow the cluster controller 110 to receive motion commands fromthe master controller 105, generally in the form of frames having atleast position, velocity, and a time stamp (PVT frames). The frames mayinclude other data, for example, a feed forward term, a gain term, orboth as will be described below. Random access memory 315 and programstorage 320 may also operate individually or together to buffer framesas they are received.

Under program control, the cluster controller 110 may operate on thedata included in the frames using real time control algorithms,including dynamic models of the axes it controls, in order to calculatetorque commands for the remote controllers 115 that are part of itsparticular cluster. The cluster controller 110 may acquire data from theremote controllers 115, for example, actual axis positions, errorindications, etc., and may report the data to the master controller 105.

The structure and operation of a remote controller 115 and an autonomousremote controller 150 will be described while referring to FIG. 4. Whilea single remote controller 115, 150 will described, it should beunderstood that the clustered architecture control system 100 mayinclude a plurality of remote controllers 115 and autonomous remotecontrollers 150. For purposes of this discussion, remote controllers 115and autonomous remote controllers 150 will be referred to as remotecontrollers 115, 150. In some embodiments a remote controller 115 mayhave the capability to operate as an autonomous remote controller 150,and an autonomous remote controller 150 may have the capability tooperate as a remote controller 115.

Remote controller 115, 150 generally operates to drive, and to receiveposition information from, one or more axes. In particular, the remotecontroller may be capable of single or multi-axis control, driving oneor more current loops, for example for powering motor windings,generally implementing a motion control loop, and collecting data inreal time. The remote controller 115, 150 may receive commands from andmay provide information to the master controller 105 or a clustercontroller 110.

The remote controller 115, 150 may include a processor 405, asemiconductor memory device 410, non-semiconductor memory 415, and anetwork interface 420. The remote controller 115, 150 may also includecircuitry 425 and drivers 430 for applying power to one or more axes 125(FIGS. 1,1 a-1 b). The remote controller 115, 150 may further includecircuitry 435 for receiving axis position information 440 from each ofthe one or more axes 125. The position information may be outputs fromone or more encoders 145 that may be part of the axes 125.

Processor 405 generally operates under control of programs stored on acomputer program product, for example, a computer useable medium, suchas semiconductor memory 410 and non-semiconductor memory 415.Non-semiconductor memory 415 may include a diskette, a computer harddrive, a compact disk (CD), a digital versatile disk (DVD), an opticaldisk, or any other device capable of storing programs in the form ofcomputer readable code.

Semiconductor memory 410 and non-semiconductor memory 415, eitherindividually or in any combination, may include remote controlleroperating system programs. Semiconductor memory 410 andnon-semiconductor memory 415, either individually or in combination, mayalso include programs for constructing and exchanging messages amongnetwork nodes and may include programs that support an applicationsprogram interface among network nodes. In particular, semiconductormemory 410 and non-semiconductor memory 415, either individually or incombination, may include programs for at least one of torque modeoperation, set point mode operation, and point to point mode operationof the remote controller 115, 150. In addition, semiconductor memory 410and non-semiconductor memory 415, either individually or in combinationmay operate to buffer frames as they are received as will be describedbelow.

The remote controller 115 may operate in torque mode when controlled bya cluster controller 110. As mentioned above, the cluster controller 110generally receives data frames from the master controller and utilizesthem to calculate torque commands for the remote controllers in itscluster. Each remote controller 115 may perform control functionsnecessary to execute its respective torque commands.

For example, remote controller 115 may be pre-programmed with thecharacteristics of the axis or axes it controls, such as the number ofmotors, phases per motor, phase resistance, back EMF constant, etc.Cluster controller 110 may issue a command to remote controller 115indicating the torque that an actuator 140, for example a motor, shouldexert. Remote controller 115 may compute a voltage, current, or power tobe applied to actuator 140 for a particular time period using thepre-programmed characteristics that causes actuator 140 to exert thedesired torque.

The remote controller 115 may also provide information back to thecluster controller 110 for determining the torque commands, for example,actual positions of the axes controlled by the remote controller 115.Encoder 145 may provide remote controller 115 with raw positioninformation such as a number of encoder counts or steps, an anglemeasurement, etc. from which remote controller 115 may compute actualposition information. Thus, the combination of the cluster controller110 and the remote controller 115 may receive a smaller number ofrelatively high level commands in the form of frames from the mastercontroller 105 and then exchange a relatively high number of commandsand feedback between themselves to execute the motion directed by theframes.

When operating under control of the master controller 105, the remotecontroller may be referred to as an autonomous remote controller 150 asmentioned above. The autonomous remote controller 150 may operate in aset-point mode. In the set point mode, the master controller 105 maysend trajectory data to the autonomous remote controller 150. Forexample, the trajectory data may be in the form of PVT frames which maygenerally include a digital representation of a position, velocity, anda time stamp for a particular axis.

The autonomous remote controller 150 may execute real-time algorithms todetermine a set of associated torque commands for the axis 125 thatcause the axis to move according to the desired trajectories. Theautonomous remote controller 150 may then use the torque commands tocompute the power to be applied accordingly to actuator 140. In setpoint mode, the autonomous remote controller 150 may generally performsome of the functions of a cluster controller and may operate to closecontrol loops between itself and the axes it controls, thus conservingthe bandwidth of the communication network 120.

Alternately, an autonomous remote controller 150 may operate in a pointto point mode under control of the master controller 105. In this mode,the autonomous remote controller 150 may receive a motion command fromthe master controller 105, and perform the necessary operations toexecute the motion command. An exemplary motion command may include athree dimensional point in an axis workspace. The necessary operationsto execute a motion command may include one or more of computingtrajectories, computing torque commands, and computing the necessarypower to be applied to the motors of the axes controlled by theautonomous remote controller 150 so that the axes reach the threedimensional point.

In response to the point to point motion command the autonomous remotecontroller 150 may send an answer reporting the results of the command.The master controller 105 may then send another point to point commandwith the next three dimensional point. This exchange may proceed untilthe autonomous remote controller 150 executes a desired sequence ofmotion commands. The point to point operational mode allows the mastercontroller 105 to limit the data transmitted to the autonomous remotecontroller 150 to one end point per motion command, as opposed to anumber of data frames, thus preserving the network bandwidth. However,in the point to point operational mode, the master controller 105 loosesthe capability of precise synchronization of trajectories executed bymultiple autonomous remote controllers 150.

An exemplary application of the clustered architecture control system isshown in FIG. 5 a. A work cell 505 incorporating the control systemincludes two robots 510, 520 and two substrate aligners 515, 520. Acluster controller 540 and three remote controllers 550, 555, 560 areused to control robot 510. Similarly, another cluster controller 545 andthree remote controllers 565, 570, 575 are used to control robot 520. Amaster controller 580 controls the two cluster controllers 540, 545 aswell as autonomous remote controllers 585, 590 for the substratealigners 515, 525. The master controller 580, cluster controllers 540,545, remote controllers 550, 555, 560, 565, 570, 575 and autonomousremote controllers 585, 590 are connected by a communication network595.

The robots 510, 520 may be five axis machines with complex non-lineardynamics while the aligners 515, 525 may be two axis machines. In thisexample, the robots 510, 520 pick substrates 530, 535 from designatedlocations and place them on aligners 525, 515, respectively. Thealigners 525, 515 may scan the substrates 530, 535 for eccentricity andalignment features. After scanning, the robots 510, 520 may pick thesubstrates 530, 535 and place them elsewhere. In one embodiment, thework cell 505 may be part of the clustered architecture control system100 (FIG. 1, 1 a-1 b).

In order to maximize the throughput of the work-cell and to guaranteecollision-free operation, the motion of the machines, that is, therobots 510, 520 and the substrate aligners 515, 525, should beaccurately synchronized. There may be no dynamic coupling among any ofthe robots 510, 520 and the substrate aligners 515, 525. Each may useindependent control algorithms without real-time data sharing. However,the mechanical configuration of the robots 510, 520 introduces strongdynamic coupling among individual axes within each robot manipulator.Coordination between the individual axes of robot 510 may be managed bycluster controller 540 in combination with remote controllers 550, 555,560. Coordination between the individual axes of robot 520 may bemanaged by cluster controller 545 in combination with remote controllers565, 570, 575. Thus, cluster controller 540 and remote controllers 550,555, 560 form one cluster, and cluster controller 545 and remotecontrollers 565, 570, 575 form another cluster.

In the work cell 505 shown in FIG. 5 a, the master controller 580 maygenerally provide supervisory functions, such as motion sequencing, datacollection, event logging and error handling. In addition, it maycalculate trajectories for all motion axes in the work cell 505. In thisexample, the master controller 580 assembles the calculation resultsinto frames specific to each individual motion axis and sends them on aperiodic basis over the network 595. The cluster controllers 540, 545and the autonomous remote controllers 585, 590 recognize the frames andcommands for the axes they control and operate accordingly.

For example, the cluster controllers 540, 545 may utilize dynamic modelsof robots 510, 520 for advanced multi-input-multi-output control,calculate torque commands, and periodically send those torque commandsto the remote controllers in their respective clusters.

The autonomous remote controllers 585, 590 may be operating in a setpoint mode and may execute real-time algorithms to determine associatedtorque commands for the aligners 515, 525, respectively. The autonomousremote controllers 585, 590 may then use the torque commands to computethe power to be applied accordingly to motors within each of thealigners 515, 525.

It is important to note that the time-critical traffic associated withclosing the control loops over the network 595 is contained within eachof the two clusters without burdening the rest of the network 595,particularly the connection with the master controller 580, which wouldotherwise be subject to heavy real-time traffic associated withcentralized control algorithms.

It should be noted that the architecture allows the master controller580 to directly control the autonomous remote controllers 585, 590 whererequired. An example application is shown in FIG. 5 b. In manyapplications, the performance may be enhanced by the distributedmodel-based control method described below.

The clustered architecture control system disclosed herein is beneficialbecause each cluster controller is capable of providing highlycentralized control within the cluster it manages. High volumes ofnetwork traffic generally required for highly centralized control aregenerally limited to each cluster. Clusters may be distributed whererequired within the communication network 120 and remote controllers maybe placed in close proximity to the axes they control, reducing cablingrequirements and problems associated with running control signals overany appreciable length.

In addition, because real-time data communication exists within theclusters and because intense network traffic is generally confinedwithin the clusters, the clusters are capable of high-performancecontrol, and the architecture allows a master controller to supervise alarge number of clusters. As a result, the architecture provideshigh-performance control where required, a high level of scalability,and an efficient distribution of controllers.

One method, mentioned above, for controlling a machine such as robot 510or aligner 585 is to calculate a trajectory for each axis. As previouslymentioned, such a trajectory can be conveniently defined by a series ofposition, velocity and time values grouped into frames, referred to asPVT frames.

FIG. 6 shows an exemplary PVT frame 605. The PVT frame 605 includesposition data 610, velocity data 615, and time data 620. In oneembodiment the data is in binary format grouped together in one or morebytes. In another embodiment each of the position data 610, velocitydata 615, and time data 620 occupies four bytes. PVT frame 605 mayoptionally include header information 625 and trailing information 630,both of which may include synchronizing, identification, parity, errorcorrection, or other types of data. PVT frame 605 may include additionaldata of varying lengths or amounts between or among the header,position, velocity, time, and trailing data. It should be noted thatwhile FIG. 6 shows the various information or data in specific locationsor areas of the frame, the different types of information and data maybe located anywhere within the PVT frame 605. It should also be notedthat the PVT frame 605 is not limited to any particular length.

It is a feature of the disclosed embodiments to use these series ofvalues as inputs for a dynamic model of the controlled machine tocalculate a theoretical torque to be applied to each axis so that eachaxis follows the desired trajectory. It is also a feature of thedisclosed embodiments to use elements of the dynamic model to scalefeedback control signals used by the remote controllers for each axis.

The torque and scaling terms may advantageously account for nonlinearities and dynamic cross coupling among individual machine axes.The torque term is referred to herein as a feedforward term because itmay not be dependent on an actual state of an axis, such as position orvelocity. The scaling term is referred to as a gain term.

Using the work-cell of FIG. 5 a as an example, the master controller 580may generate a trajectory for each axis of robot 510 in terms of acommanded position, velocity and acceleration. Using an inverse dynamicmodel of the robot 510, the master controller may utilize the trajectoryinformation to generate corresponding feedforward, and gain terms. Theseterms may be grouped together with the trajectory information in framesspecific to each axis, referred to as PVT-FG frames. FIG. 7 shows anexemplary PVT-FG frame 705. PVT-FG frame 705 includes optional header710 position 715, velocity 720, time 725, and optional trailinginformation 730, similar to PVT frame 605. In addition, PVT-FG frame 705includes at least one feedforward term 735 and at least one gain term740. The data may be in binary format grouped together in one or morebytes. In one embodiment of PVT-FG frame 705 the position 715, velocity720, time 725, feedforward 735, and gain 740 terms each occupy fourbytes. Similar to PVT frame 605, PVT-FG frame 705 may include other dataof varying lengths or amounts, distributed among or between the variousterms.

The PVT-FG frames may then be distributed over the network 595. Thecluster controller 540, which receives the data, may interpolate betweentwo consecutive frames to obtain an instantaneous position, velocity,feedforward term and gain value, and utilize this information to controlthe robot 510. Similarly, the cluster controller 545 and autonomousremote controllers 585, 590 may receive corresponding data from themaster controller 580, and utilize them to control the robot 520 andaligners 515, 525, respectively.

An exemplary technique for developing the feedforward and gain termswill now be explained in detail. The following dynamic model may beused:

$\begin{matrix}\begin{matrix}{\tau_{i} = {{\sum\limits_{j = 1}^{n}{{M_{ij}\left( \left\{ \theta_{act} \right\} \right)}\left\lbrack {{\overset{¨}{\theta}}_{{cmd}\; j} + {u_{j}\left( {\theta_{{cmd}\; j},{\overset{.}{\theta}}_{{cmd}\; j},\theta_{{act}\; j}} \right)}} \right\rbrack}} +}} \\{{h_{i}\left( {\left\{ \theta_{act} \right\},\left\{ {\overset{.}{\theta}}_{act} \right\}} \right)}} \\{= {{\sum\limits_{j = 1}^{n}{{M_{ij}\left( \left\{ \theta_{act} \right\} \right)}{u_{j}\left( {\theta_{{cmd}\; j},{\overset{.}{\theta}}_{{cmd}\; j},\theta_{{act}\; j}} \right)}}} +}} \\{{{\sum\limits_{j = 1}^{n}{{M_{ij}\left( \left\{ \theta_{act} \right\} \right)}{\overset{¨}{\theta}}_{{cmd}\; j}}} + {h_{i}\left( {\left\{ \theta_{act} \right\},\left\{ {\overset{.}{\theta}}_{act} \right\}} \right)}}}\end{matrix} & (1)\end{matrix}$

where _(i) denotes torque applied to axis i, _(acti) and _(cmdi) areactual and commanded positions of axis i, respectively, {_(act)} and{_(cmd)} stand for position vectors defined as{_(act)}={_(act1, act2, . . . , actn)}^(T) and{_(cmd)}={_(cmd1, cmd2, . . . , cmdn)}^(T) M_(ij) is an inertia matrixelement indicating inertial cross-coupling between axes i and j, h_(i)is a function including other position- and velocity-dependent dynamiceffects for axis i, such as centrifugal, Coriolis and gravity terms,u_(i) stands for control law output for a unit-inertia systemcorresponding to axis i, i varies from 1 to n, n is the total number ofaxes or degrees of freedom, and dot and double-dot indicate first andsecond time derivatives, respectively.

Provided that position and velocity tracking errors are small, theactual positions and velocities can be approximated with commandedquantities. Furthermore, neglecting the M_(ij)u_(i) terms for i≠j, thedynamics of Equation (1) can be rewritten and approximated as thefollowing inverse dynamic model:

$\begin{matrix}{{{\tau_{i} = {{{{M_{ii}\left( \left\{ \theta_{cmd} \right\} \right)}{u_{i}\left( {\theta_{{cmd}\; i},{\overset{.}{\theta}}_{{cmd}\; i},\theta_{{act}\; i}} \right)}} + {\sum\limits_{j = 1}^{n}{{M_{ij}\left( \left\{ \theta_{cmd} \right\} \right)}{\overset{¨}{\theta}}_{{cmd}\; j}}} + {h_{i}\left( {\left\{ \theta_{cmd} \right\},\left\{ {\overset{.}{\theta}}_{cmd} \right\}} \right)}} = {{G_{i}u_{i}} + F_{i}}}}\mspace{79mu} {where}\text{:}}\mspace{79mu}} & (2) \\{\mspace{79mu} {G_{i} = {M_{ii}\left( \left\{ \theta_{cmd} \right\} \right)}}} & (3) \\{\mspace{79mu} {F_{i} = {{\sum\limits_{j = 1}^{n}{{M_{ij}\left( \left\{ \theta_{cmd} \right\} \right)}{\overset{¨}{\theta}}_{{cmd}\; j}}} + {h_{j}\left( {\left\{ \theta_{cmd} \right\},\left\{ {\overset{.}{\theta}}_{cmd} \right\}} \right)}}}} & (4)\end{matrix}$

The above expressions for G_(i) and F_(i) define the gain andfeedforward terms, respectively. The index i indicates which axis thefeedforward and gain terms will be applied to. In order to furtherimprove control performance, a disturbance observer may be utilized foreach axis to compensate for the simplifications made.

The trajectory and inverse dynamic model computations for the controlledmachine, in this example robot 510, may be performed by mastercontroller 580. When values for G_(i) and F_(i) have been determined,master controller 580 may assemble PVT-FG frames for each axis anddistribute them over the network 595 to the cluster controller 540 ofthe robot 510.

Cluster controller 540 of robot 510 may have instructions and algorithmsstored in its memory to operate the robot 510, for example, by sendingtorque commands and receiving feedback signals between itself and theremote controllers 550, 555, 560. Using the PVT-FG frames from themaster controller 580, the cluster controller 540 calculates enhancedtorque commands for each axis controlled by remote controllers 550, 555,560. The torque commands are said to be enhanced because the inversedynamic model of Equation 2 and the resulting G_(i) and F_(i) terms fromEquations 3 and 4, respectively, at least include elements and functionsthat represent inertial cross coupling between axes (e.g. M_(ij)) andposition and velocity dependent effects (e.g. h_(i)). Thus, the clustercontroller 540 calculates the torque commands using the G_(i) and F_(i)terms, resulting in torque commands that more accurately control themotion of the axes with which they are associated.

Once the enhanced torque commands have been calculated, the clustercontroller 540 may then distribute them to the appropriate remotecontroller 550, 555, 560. Remote controllers 550, 555, 560 may generallybe pre-programmed with the characteristics of the axes they control,such as the number of motors, phases per motor, phase resistance, backEMF constant, etc. In response to the enhanced torque commands, remotecontrollers 550, 555, 560 may compute the proper voltages, currents, orpower to be applied to the motors they control.

Various algorithms including those using Equation 2, Equation 1, and aconventional single-input-single-output (SISO) feedback algorithm wereapplied to a five-axis robot similar to robot 510 to compare trackingerrors and to verify the efficacy of the exemplary technique fordeveloping the gain and feed forward terms, G_(i) and F_(i),respectively. The five-axis robot was a type generally utilized forautomated pick-place operations in semiconductor manufacturingapplications. The five-axis robot included an articulated arm with twoend-effectors operating in parallel horizontal planes complemented by avertical lift drive. This particular application represented achallenging test bed since the dynamics are highly non-linear withstrong cross-coupling among axes. Among other operations, the five-axisrobot was commanded to perform a straight-line extension move of a firstend-effector in the radial direction.

FIG. 8 shows the measured tracking error of the first end-effector, inparticular its normal component which indicates the deviation of thefirst end-effector from the desired straight-line path, for each appliedalgorithm. It is observed that the tracking performance of the algorithmusing Equation 2 (810) closely approaches the performance of thealgorithm using Equation 1 (820), and clearly outperforms theconventional single input single output feedback algorithm (830).

As mentioned previously with respect to the clustered architecturecontrol system 100, it is important to accurately synchronize the axesof the system to maximize throughput and to guarantee collision-freeoperation.

It is a feature of the disclosed embodiments to synchronize operationscontrolled by the clustered architecture control system 100 bymaintaining a common, accurate time reference on each of the networknodes, and by time stamping all time dependent network traffic. Inparticular, PVT and PVT-FG frames are stamped with a time at which theaction described by the frame should occur, thus ensuringsynchronization of axis motions across the communication network 120.

Referring to FIG. 2, the master controller 105 includes time keepingcircuitry 260 which may have a high resolution register 265 and a lowresolution register 270. The master controller may also include timingcontrol circuitry for performing other operations associated withmaintaining a common time reference among the network nodes. Referringto FIG. 3, each cluster controller 110 may also have time keepingcircuitry 340 with a high resolution register 345 and a low resolutionregister 350. Referring also to FIG. 4, each remote controller 115 andautonomous remote controller 150 also may have time keeping circuitry450 including a high resolution register 455 and a low resolutionregister 460.

In order to maintain a common time reference, the master controller mayissue “cycle start” messages at the beginning of each bus cycle on thecommunication network 120. An exemplary bus cycle may occupyapproximately 125 usec and may begin with the “cycle start” messagefollowed by intervals for isochronous traffic and asynchronous traffic,as shown in FIG. 9 a. FIG. 9 b shows an exemplary cycle start message,and FIG. 9 c shows an exemplary high resolution register 265, 345, 455.

Referring back to FIG. 2, the network interface 230 may generallyprovide a mechanism for automatically updating the high resolutionregisters 265, 345, 455 based on each cycle start message.

Each network node may also include a mechanism that provides interruptswhen a new isochronous cycle has started, that is when the low order bitof the high resolution register toggles, and when 64 seconds haveexpired, indicating that the 7^(th) bit of the high resolution registerhas changed. When the communication network 120 is an IEEE 1394 network,some or all of the features described above may be provided according tothe IEEE 1394 standard. In an IEEE 1394 network the high resolutionregisters may be referred to as CYCLE_TIME registers and the lowresolution registers may be referred to as BUS_TIME registers.

Network synchronization may be achieved as follows. After thecommunication network 120 has been initialized or reset, the mastercontroller 105 may assume control over the communications network 120and may maintain the low resolution register 270 utilizing time keepingcircuitry 260 and timing control circuitry 275. Each cluster controller110, remote controller 115, and autonomous remote controller 150 maysynchronize its own low resolution register 350, 460 with the lowresolution register 270 on the master controller 105 on initializationor reset. Each cluster controller 110, remote controller 115, andautonomous remote controller 150 then maintains and updates its lowresolution register 350, 460 based on its high resolution register 345,455. The communication network 120 itself may generally providefacilities for automatic synchronization of the high resolutionregisters 265, 345, 455 across the communication network 120. The mastercontroller 105 sends PVT or PVT-FG frames to the cluster controllers 130or to the autonomous remote controllers 150.

In the synchronized system disclosed herein, the PVT or PVT-FG framesinclude a time stamp which indicates when in the future the PVT orPVT-FG frame should be executed. Upon reaching the indicated time, thecluster controllers 130 and autonomous remote controllers 150 operatetheir respective axes according to the information received in theframes.

In summary, a common time reference is maintained among the mastercontroller 105, the cluster controllers 110, the remote controllers 115,and the autonomous remote controllers 150. By maintaining the commontime reference and time stamping the PVT and PVT-FG frames with a timeat which the action described by the frame should occur, synchronizationof axis motions across the communications network 120 may be accuratelysustained.

As mentioned above, a lightweight IEEE 1394 protocol has been developedfor industrial control devices, referred to as the Instrument andIndustrial Control Protocol (1394TA IICP, referred to as “IICP”).

The IICP and other similar protocols may provide flow control, aframework for creating and closing communication connections amongsystem components, a mechanism for reactivating connections after busreset, and a mechanism of resolving PHY addresses to communicationconnections, from a master controller, thus removing the burden ofenumerating the network from the remote controllers. In addition,communication connections may persist over a bus reset event when usingthese types of protocols.

It is a feature of the disclosed embodiments to provide extensions tothe protocol being used that include a usage scheme and a message formatfor exchanging information among the master controller 105, the clustercontrollers 110, and the autonomous remote controllers 115. The usagescheme and message format are referred to collectively as the protocolextensions.

The network protocol extensions described herein are advantageous inthat they provide a specific message framework for network communicationmessages. The contents of the messages may be transparent to thetransfer protocol employed.

An exemplary structure of the type of protocol being used in the controlsystem 100 is shown in FIG. 10. The protocol may include an applicationlayer 1105, a connection layer 1110, and a transaction layer 1115. Theapplication layer 1105 uses the facilities of the connection layer 1110and assumes that point to point connections, referred to as plugs, areestablished between a master device, such as the master controller 105(FIG. 1, 1 a-1 b) and a remote device, such as a remote controller 150(FIG. 1,1 a-1 b).

FIG. 11 shows an example of how these plugs may be implemented. Themaster device may open one or more plugs 1020 to each of the remotedevices. A plug 1020 provides one or more ports 1025, 1030. Each port1025, 1030 provides means for sending frames, such as PVT or PVT-FGframes, where the frames are opaque pieces of data from the port'sperspective. A port 1025, 1030 generally operates in a duplex mode, i.e.data can be concurrently sent in both directions. The application layer1105 may use the ports as a control port 1030 or a data port 1025.Messages on the control port 1030 generally have meta data incorporatedin the header of the message, describing the content of the message.Data port messages generally lack such metadata. The remote controller150 and the master controller 105 are generally made aware of the dataport message structure through programming, predetermined tables,definitions, or by other means. Messages on a control port 1030 maydefine the content of, or otherwise identify messages on one or moredata ports 1025. In some embodiments this may allow data port messagesto be sent without header information or any message definition,lowering the overhead associated with sending such messages. Theinteraction between the control and data ports may be isolated to aparticular plug, or messages on a particular control port may providecontrol for data ports of other plugs opened to the same or differentremote devices.

It should be understood that the protocol extensions described in thedisclosed embodiments are not limited in use to a particular protocolbut may be used with any protocol that supports plugs.

The application layer extensions described herein utilize a layeredapproach that may include relatively simple control port message types.The extensions may also provide a framework for vendor specificextensions, that is messages that may be tailored specifically for aparticular device manufacturer's component. This facilitates the use ofvendor specific application layer command sets, wrapped in a number ofcontrol port message types. Data port message format may also be vendorspecific.

A control port 1030 may generally exchange commands and responsesbetween system components. A data port 1025 may transmit data frameswhich are addressed to specific objects on a remote controller or themaster controller. Addressing may generally be implied from the portdesignation and may not be part of the message. The data port messagestructure may generally be vendor specific.

An exemplary control message structure 1700 is presented in FIG. 17. AQuadlet 1705 may denote a 32-bit wide piece of data. The D field 1710may designate a direction, indicating whether the message is sent, forexample, from the master controller 105 to a remote controller 150, orvice versa. The message type 1715 may designate a defined message typeexplained below. Up to 2̂15 message types may be defined. The Message IDfield 1720 may be used for matching commands and response fortransaction-like messages, for example, ACTION type messages. Forstream-like messages, for example, STRING type messages, the Message IDfield 1720 may be used to provide additional ordering information.ACTION and STRING type messages will be explained below. In someembodiments the Message ID field 1720 may be optional. The Reservedfield 1725 may provide a placeholder for vendor specific extensionswithin the message header. Some specific control port messages mayinclude ACTION, EVENT, and STRING type messages. The messages sent onthe control port of a plug may all have similar structure. It is afeature of the disclosed embodiments that these message types may berelatively few, allowing a significant flexibility on the remotecontroller level in the implementation of specific commands. Forexample, all commands for setting and getting parameters may be ACTIONcommands, where the actual parameter to be set/get as well as the formatof the data may be further defined by the remote controllermanufacturer. Thus, remote controller manufactures may only be requiredto implement a very limited command set in order to be compliant withthe control system.

An exemplary ACTION message 1800 is shown in FIG. 18. The ACTION message1800 may be used to send commands to remote controllers and for remotecontrollers to send responses to previously sent commands from themaster controller. A response to a previously sent ACTION command maygenerally copy the header of the command except for the D field 1810.For ACTION commands the Message ID field 1820 may be required. Theformat of the body of the message may be specific to a particular remotedevice vendor.

ACTION messages may be used for setting, getting, or storingconfiguration parameters on a remote device such as a remote controller,configuring one or more data ports for tracing, event, status, PVT orother application specific operations, operating I/O on a remote device,sending motion commands for discrete moves when trajectory is generatedon the remote device, and for sending any other distinct command thatthe remote device supports, e.g. for configuration, diagnostics ortransitioning the device to a another operational state. ACTION messagesmay be vendor specific.

In ACTION response messages from a remote device to the mastercontroller, the reserved field 1825 may include an 8-bit vendor specificresult code. With this provision, responses to ACTION commands that onlyinclude a result code can be implemented by sending only a header inresponse. Commands for setting parameter values in the remote device arean example of such a mode of operation.

The vendor specific header 1830 may indicate one of set, get, or storefor a specific device parameter. The Axis ID field 1835 provides furtherdispatching for up to 256 axis (or instances) for the specific deviceparameter for a specific device. The Vendor command ID 1840 may indicatea vendor specific device parameter or command. The Vendor command ID1840 may support up to 2̂16 individual commands or parameters. The Vendorspecific command parameters 1 . . . n 1845 may provide one or moreoptional parameters in a command or a response.

An exemplary EVENT message structure 1900 is shown in FIG. 19. The EVENTmessage 1900 is used to send event data from the remote controller tothe master controller. The EVENT message may also provide mechanism forusing a control port message instead of opening a separate plug for agiven application specific data transfer. Event data may be sent throughEVENT messages in lieu of opening an event specific plug.

The Message ID field 1920 in the message header is used to indicate avirtual event connection number. The value in this field may be aparameter in a vendor-specific “add parameter to event” control message.

An example of a vendor specific EVENT message 2000 is presented in FIG.20. In this example, up to 6 virtual event connections may be set up.The number of event parameter fields, in this example, “Event parameter1 . . . 6 (2045), depend on the specific drive parameter that is setupfor event capture. These fields represent parameter values at theoccurrence of the event. The event parameter fields contain 0 if a givenparameter is not set for event capture. For this particular devicemanufacturer, up to 6 parameters can be configured as event parameters.

The STRING message type is used to create a virtual serial channel fromthe master controller to the remote controller and vice versa by sendingunformatted text data. An example of a STRING message structure 2100 isdepicted in FIG. 21.

The message ID 2120 may increase sequentially with every message sentfrom the remote device or the master controller (these counters increaseindependently) and provides additional means of sequencing the trafficif the messages are received out of order.

An exemplary vendor specific STRING command 2200 is presented in FIG.22. In this example, the series of message bodies 2245 may each comprisefour characters. The remote device for this example may support up to 6quadlets of message body information and may encode characters usingplain text ASCII encoding.

Data port message structures may generally represent pure data and mayhave no header. They may also be remote device vendor specific andshould be interpreted in that context. The remote device manufacturer inthis example uses PVT Status and TRACE message types. Other messagetypes may also be used.

An exemplary PVT or PVT-FG message structure 2300 is shown in FIG. 23.The PVT message may generally represent one trajectory set point along amotion path. As previously mentioned, a PVT or PVT-FG message isgenerally sent from the master controller 105 to one or more clustercontrollers 110 or autonomous remote controllers 150. The PVT or PVT-FGmessages are used to send time-stamped trajectory set point data.Optionally, the PVT or PVT-FG messages may also include a torque limitterm. The PVT or PVT-FG messages may also be used to send a periodictimestamp when the receiving cluster controller 110 or autonomous remotecontroller 150 is in a pre-operational state. The PVT or PVT-FG messagemay be sent at a periodic rate, for instance 100 Hz. In one embodiment,the PVT message includes a commanded position 2305, a commanded velocity2310, and the network time 2315. The PVT or PVT-FG message mayoptionally include one or more of a feed forward term 2320, a gain term2325, and a torque limit term 2330.

The STATUS message may generally present the remote device state at thetime the STATUS message was generated. An example of a STATUS message2400 is depicted in FIG. 24.

The STATUS message is generally sent from the one or more clustercontrollers 110 or autonomous remote controllers 150 to the mastercontroller 105. The STATUS message may be used to send time-stampedstatus, actual position and velocity data from one or more clustercontrollers 110 or autonomous remote controllers 150 to the mastercontroller 105.

Optionally, the STATUS message may be used to send time-stamped I/Odata. The STATUS message may be sent at a periodic, for instance 100 Hz,rate or may be sent at an acyclic rate for low-latency I/O eventcapture. In one embodiment, the STATUS message includes an actualposition 2405, states of various digital I/O devices 2410, a timestamp2415, a commanded position 2420, an actual velocity 2425.

The status word 2430 contains information about the driveerror/fault/warnings state. It contains also information about the stateof the remote device PVT buffer (flow-control information).

An exemplary TRACE message 3200 is presented in FIG. 32. A TRACE messagecan contain up to n sampling records, each record may have up to msamples. The frame should comply also with the following device-specificconstraints:

n*m<=128

m<=6

The TRACE_message 3200 is generally sent from the one or more clustercontrollers 110 or remote controllers 115, 150 to the master controller.The TRACE_message 3200 is used to send time-stamped, periodicallysampled, diagnostic data to the master controller 105. The TRACE_message3200 may be sent at a periodic or variable rate of up to, for example,16 kHz, and may be settable through an ACTION command. The structure ofthe data and other parameters of the trace (trigger, delay, samplingrate, etc.) is also settable through ACTION commands. In addition, likesome of the other messages, the TRACE_message 3200 may be sent through aplug specifically opened to support high resolution data transfer. Inone embodiment, the TRACE_message includes a number of trace variables3205.

The protocol extensions of the disclosed embodiments may includespecific implementations of the TRACE_message that may include suchmessage types as PVTFG, HIRES_POS, and HIRES_VEL messages. The STATUSmessage described above may also constructed as a specificimplementation of a TRACE message.

As previously mentioned, a PVT or PVT-FG message is generally sent fromthe master controller 105 to one or more cluster controllers 110 orautonomous remote controllers 150. The PVT or PVT-FG messages are usedto send time-stamped trajectory set point data. Optionally, the PVT orPVT-FG messages may also include a torque limit term to support a teachmode, as will be described in detail below. The PVT or PVT-FG messagesmay also be used to send a periodic timestamp when the receiving clustercontroller 110 or autonomous remote controller 150 is in apre-operational state. The PVT or PVT-FG message may be sent at aperiodic, for instance 100 Hz, rate. In one embodiment, the PVT messageincludes a timestamp of 4 bytes, a commanded position of 4 bytes, and acommanded velocity of 4 bytes. The PVT-FG message may optionally includeone or more of a feed forward term of 4 bytes, a gain term of 4 bytes,and a torque limit of 4 bytes.

A HIRES_POS message is generally sent from the one or more clustercontrollers 110 or autonomous remote controllers 150 to the mastercontroller 105. The HIRES_POS message is used to send time-stamped,periodically sampled, actual position from one or more nodes to themaster controller. The HIRES_POS message may be sent at a periodic orvariable rate of up to, for example, 16 kHz, and may be settable throughan ACTION command discussed below. In addition, the HIRES_POS messagemay be sent through a plug opened specifically for high resolution datatransport. In one embodiment, the message includes a block having atimestamp of 4 bytes and an actual position of 4 bytes. The block may berepeated up to 16 times, representing 1 ms worth of data at a 62.5sampling rate, with a total length up to 128 bytes.

In an alternate format, the HIRES_POS message may include a timestamp of4 bytes, and a repeating actual position field of 4 bytes, that mayrepeat up to 16 times representing 1 ms worth of 16 kHz sampled data.The message may be constructed with one timestamp per frame assumingthat samples are equally spaced with the sampling rate, and that thefirst position field is sampled at the time specified in the stamp.

A HIRES_VEL message is generally sent from the one or more clustercontrollers 110 or autonomous remote controllers 150 to the mastercontroller 105. The HIRES_VEL message is used to send time-stampedstatus, and periodically sampled actual velocity data to the mastercontroller 105. The HIRES_VEL message may be sent at a periodic orvariable rate of up to, for example, 16 kHz, and may be settable throughan ACTION command discussed below. In addition, the HIRES_VEL messagemay be sent through a plug opened specifically to support highresolution data transfers. In one embodiment, the HIRES_VEL message mayinclude a timestamp of 4 bytes and an actual velocity of 4 bytes.

In addition to carrying information from the cluster controllers 110 andautonomous remote controllers 150 to the master controller 105, STATUS,HIRES_POS and HIRES_VEL messages in accordance with the abovedescription may be sent from one or more remote controllers 115 to oneof the cluster controllers 110 or to the master controller 105.

Thus, the disclosed embodiments include protocol extensions, that is, aunique message set for exchanging information among the mastercontroller 105, cluster controllers 110, remote controllers 115, andautonomous remote controllers 150. The unique message set isadvantageous because it provides additional functionality for theclustered architecture control system 100 over and above the servicesprovided by a standard network protocol, for example, the 1349TA IICP.

In a control system such as the clustered architecture control system100 it may be advantageous to capture instantaneous axis or othercharacteristics from one or more of the cluster controllers 110 orremote controllers 115, 150 upon the occurrence of a particular event.FIG. 12 shows a work cell 1200 where such a feature may be beneficial.Work cell 1200 includes a robot 1210 with a cluster controller 1215 andthree remote controllers 1230, 1235, 1240. The cluster controller 1215communicates with a master controller 1245 through communicationsnetwork 1250. In one embodiment, the work cell 1200 may be part of theclustered architecture control system 100 (FIGS. 1, 1 a-1 b).

As an example, “on the fly” recognition and correction for eccentricityor misalignment of a circular payload, such as a semiconductor substrate1205, carried by the robot 1210, may require instantaneous data capture.In this case, the robot 1210 may move through a set of stationarysensors 1216 which detect the leading and trailing edges of the payload1205. Remote controllers 1230, 1235, 1240 may capture certaincharacteristics, such as the positions and velocities of each axis ofthe robot 1210, and provide the data to master controller 1245. Themaster controller 1245 may then determine the position of the robot'send-effector 1220 as the payload edges are detected, and then determinethe actual location of the center of the payload 1205. Once the payloadcenter is determined, the master controller 1245 may alter thetrajectory of the robot 1210 so that the payload 1205 is delivered in acentered manner regardless of the amount and direction of the initialeccentricity.

In another example, the robot 1210 may include one or more interlocks1225 coupled to cluster controller 1215. If an interlock 1225 is trippedfor some reason, it may be important to determine the positions of therobot's axes and the positions of other equipment the robot 1210 may beinteracting with at the time the interlock 1225 is tripped.

It is a feature of the disclosed embodiments to capture instantaneousdata from a set of axes of the clustered architecture control system 100upon the occurrence of, or associated with, a triggering event. Whilethe procedures described below generally include the master controller1245, it should be understood that a cluster controller or remotecontroller with appropriate processing power and memory may also performthe functions provided by the master controller 1245.

Referring to FIG. 12 and to the flow chart of FIG. 13, an instantaneousdata capture sequence may proceed as follows. The remote controllers1230, 1235, 1240 may be instructed to recognize certain events astrigger events, for example, a changing output state of one or more ofthe sensors 1216, as shown in blocks 1305 and 1306. The remotecontrollers 1230, 1235 1240 may also be instructed to communicate with aspecified set of nodes upon the occurrence of a particular event asshown in block 1310. The remote controllers 1230, 1235 1240 may furtherbe instructed to buffer one or more particular quantities of interest,for example, an axis position or velocity, at a specified sampling rate,typically lower than that of the servo loop used to control a particularaxis, as shown in blocks 1315 and 1316. Thus, at least in oneembodiment, every data point of a quantity of interest may not besampled. The instructions may be part of each remote controller'soperating system or instructions may be provided from cluster controller1215 or master controller 1245. The quantity of interest, triggerevents, and specified set of nodes may be different for each remotecontroller.

Once instructed, remote controllers 1230, 1235 1240 begin buffering data(block 1320) and observing for trigger events (block 1325). Uponoccurrence of the trigger event, the remote controller recognizing theevent records the time of the event as shown in block 1330, and as shownin block 1335, sends a message with the event time information to thespecified set of nodes for the particular event. The specified nodesinterpolate their buffered quantities of interest to determine a valuefor the quantities at the event time as shown in block 1340. Thespecified nodes send the interpolated values of the quantities ofinterest to the master controller as shown in block 1345. The mastercontroller may then use the data to alter trajectories or operationswithin the system as shown in block 1350.

In some cases, direct communication among the remote controllers may notbe desirable, e.g., due to a large number of plugs required. In thiscase, the master controller may distribute the event time to thespecified nodes.

An instantaneous data capture data procedure modified to accommodateevent time distribution by the master controller may proceed as follows.Referring now to FIGS. 12 and 14, the remote controllers 1230, 1235,1240 may be instructed to recognize certain events as trigger events asshown in blocks 1405 and 1410, for example, a changing output state ofone or more of the sensors 1216. The remote controllers 1230, 1235, 1240may be instructed to buffer one or more particular quantities ofinterest as shown in blocks 1411 and 1415, for example, an axis positionor velocity, at a specified sampling rate, typically lower than that ofthe servo loop used to control a particular axis. Once instructed,remote controllers 1230, 1235 1240 begin buffering data (block 1420) andobserving for trigger events (block 1425).

Upon occurrence of the trigger event, the remote controller recognizingthe event records the time of the event as shown in block 1430 and sendsa message with the event time information to the master controller 1245as shown in block 1435. The master controller 1245 then sends the eventtime to the set of nodes specified for the particular event as shown inblock 1440. In block 1445, the specified nodes interpolate theirbuffered quantities of interest to determine a value for the quantitiesat the event time. As shown in block 1450, the specified nodes send theinterpolated values of the quantities of interest to the mastercontroller 1245. The master controller 1245 may then use the data toalter trajectories or operations within the system 1200, as shown inblock 1455.

As another alternative, if one or more remote controllers do not possessufficient resources for data buffering and interpolation, for example,due to limited memory or computational power, these operations may alsobe performed by the master controller. However, this approach may resultin an increase in communication network traffic.

With reference to FIGS. 12 and 15, an instantaneous data captureprocedure modified to accommodate data buffering and interpolation bythe master controller 1245 may proceed as follows. As shown in blocks1505 and 1506, the remote controllers 1230, 1235, 1240 may be instructedto recognize certain events as trigger events, for example, a changingoutput state of one or more of the sensors 1216. As shown in blocks 1510and 1511, the remote controllers 1230, 1235, 1240 may also be instructedto monitor one or more particular quantities of interest, for example,an axis position or velocity, at a specified sampling rate, typicallylower than that of the servo loop used to control a particular axis.Once instructed, the remote controllers 1230, 1235, 1240 begin toperiodically send the monitored quantities of interest to the mastercontroller 1245 (block 1515), which stores them for a specified periodof time, e.g., using a circular buffer, as shown in block 1520. At thesame time, the remote controllers 1230, 1235, 1240 also begin monitoringfor trigger events as shown in block 1525 As shown in block 1530, uponoccurrence of the trigger event, the remote controller recognizing theevent records the time of the event and as shown in block 1535, sends amessage with the event time information to the master controller 1245.As shown in block 1540 the master controller 1245 then interpolates thebuffered quantities of interest to determine a value for the quantitiesat the event time. The master controller 1245 may then use the data toalter trajectories or operations within the system 1200 as shown inblock 1545.

While in the procedures described above the remote controllers areassumed to recognize trigger events, observe for them and record timewhen they occur, it should be understood that an autonomous remotecontroller, cluster controller or master controller may also performthese functions described above with reference to the remotecontrollers.

In many event capture applications, in particular for instantaneousposition capture purposes, the resulting data include errors due totransition delays of the sensors that trigger the events. These errorsbecome particularly significant in high-speed/high-accuracy applicationswhere the axes of the controlled machine may travel an undesirably longdistance from the time when an event physically occurs to the point whenthe event is signaled to the control system.

In the example above of “on the fly” recognition and correction foreccentricity or misalignment of the circular payload 1205, theend-effector 1220 of the robot 1210 may travel an undesirably longdistance from the location where the edge of the payload passes throughthe sensors 1216 to the location where the trigger event is recognizedand where the time is recorded. Assuming that the signal transitiondelays are deterministic, these errors can be minimized by a simpledelay-compensation mechanism described below.

In order to estimate the length of motion between the location where anevent occurs to the location where it is actually recognized by thecontrol system, velocity information needs to be captured in addition toposition data. Assuming that the velocities of the axes of interestremain substantially constant between the two locations, and providedthat the time elapsed is equal to a known time delay, the motion of theaxes of interest between the two locations can be reconstructed toobtain an estimate of the actual position of each axis at the timeinstant when the event physically occurred using the followingexpression:

θ_(acti)=θ_(i)−{dot over (θ)}_(i) τ,i=1,2, . . . ,m  (5)

where θ_(acti) denotes actual position of axis i when the positioncapture event occurred, θ_(i) and {dot over (θ)}_(i) represent positionand velocity of axis i, respectively, as captured by the control system,τ is sensor transition delay, and m indicates the number of axes ofinterest.

Although the transition delay of a sensor is typically included in thespecifications, the actual latency often depends on the particularconditions in which the sensor is used. Consequently, a more accuratevalue of the transition delay may need to be obtained through acalibration process. Referring to FIGS. 12 and 16, an example involvinga single axis of motion will be explained. The work cell 1200 of FIG. 12may also include at least one aligner 1250 having an axis 1270controlled by an autonomous remote controller 1255. The autonomousremote controller 1255 is in turn controlled by the master controller1245. A notched substrate 1260 may have been placed on the aligner 1250and the aligner may also have circuitry 1265 including sensors fordetecting the position of the notch in the substrate 1260. As shown inblock 1605 the autonomous remote controller 1255 may move the axis 1270to trigger a position capture event, in this example, the circuitry 1265sensing the notch in the substrate 1260. The autonomous remotecontroller 1255 moves the axis 1270 at a regular speed of operation andas shown in block 1610 records the instantaneous position and velocityof the axis 1270 when the circuitry 1265 detects the event. As shown inblock 1615 the autonomous remote controller 1255 then moves the axis1270 in the same direction to repeat the event at a substantially lowerspeed, which is selected so that the distance traveled by the axis 1270in the time interval corresponding to the transition delay of thecircuitry 1265 is smaller than the required position capture accuracy.As a result, the position error due to any transition delays may beneglected. Again, as shown in block 1620, the instantaneous position ofthe axis 1270 is captured when the circuitry 1265 detects the event. Asshown in block 1625 the resulting data can be used to estimate thecircuitry transition delay by solving Equation (5) for τ, where θ_(acti)is approximated by the position capture result at the low speed, andθ_(i) and {dot over (θ)}_(i) are the event capture results at theregular speed of operation.

If combined motion of multiple axes is involved in the position captureevent, the calibration procedure needs to take into account thegeometrical configuration of the sensor(s) and moving component(s) ofthe system. An example calibration procedure for such a case can befound in commonly assigned U.S. patent application Ser. No. 10/739,375,incorporated by reference, where a position capture mechanism isutilized for on-the-fly recognition of eccentricity of a payload.

If the position capture event is triggered by motion of a controlledmachine, for example the aligner 1250, the calibration process may befully automated by the control system.

Thus, the disclosed embodiments provide a number of methods forcapturing data about particular quantities of interest in the clusteredarchitecture control system. The methods are advantageous in that theydo not require a communication network with extremely low latency, whichmay be necessary to propagate trigger events among network nodes. When atriggering event occurs, the controller recognizing the event recordsthe event time. The data around the event time from one or more axes maybe interpolated to yield computed data values for the event time. Thecomputed data values may be used to alter trajectories or operationswithin the system 1200. A calibration procedure is also provided toaccount for discrepancies between the time an event occurs and the timethe event is recognized by the control system.

Robots requiring unlimited rotation may use slip rings orinductive/capacitive feed throughs to connect signal or power throughthe rotatable connection. As frequencies and bandwidth increase thesetypes of connections become increasingly difficult to implement and tomaintain. In the case of vacuum robots, slip rings may present a sourceof contamination. For robots mounted on cars or traversers providingcommunications and power generally requires cables with service loops.In addition, service connections to system components generally requireconnectors and associated cables.

It is a feature of the disclosed embodiments to utilize wirelessconnections to provide communications among system components in orderto eliminate problems due to physical attributes of cabling, slip rings,feed throughs and various mechanical connections, to lower maintenancerequirements in comparison to wired connections, and for increasedreliability.

Referring to FIGS. 1(1 a-1 b), communication network 120 may include oneor more wireless sections that provide a communication path among one ormore of the master controller 105, the cluster controllers 110, theremote controllers 115 and autonomous remote controllers 150.

FIG. 25 shows a portion of the clustered architecture control system 100in which a wireless connection has been implemented. A robot 2505 mayinclude multiple axes and may be controlled by a cluster controller 2510and three remote controllers 2515, 2520, 2525. The master controller 105(FIGS. 1 (1 a-1 b), shown here again) controls the cluster controller2510 through communication network 120. In this embodiment, the clustercontroller 2510 and the communication network 120 have correspondingwireless interfaces 2530, 2535 that provide a wireless connection 2540between them. The wireless interfaces 2530, 2535 may provide anysuitable wireless communication protocol or signaling technique orstandard, for example TDMA, CDMA, IEEE 802.xx, CIP protocol, Bluetooth,close range RF, optical, etc. The selected wireless protocol may includesecurity features such as encrypted transmissions in order to preventtampering.

In addition, other communication paths, for example, among controllers,axes, end effectors, and service connections may also be wireless. Stillfurther, in a robotized automation system, loadports, fan systems,filter units, etc. may also utilize wireless connections. The wirelessconnections are advantageous because they allow communications withoutinvading a component's surroundings with a cable. For example, a fieldservice technician may connect to a component without having to enterthe component's workspace. Utilization of wireless connections andprotocols generally simplifies component connections and, in someinstances, only power connections may require cabling.

The disclosed control system 100 may by required to accommodate a humanpresence in the workspace of each of the components and may includefunctions that ensure system integrity.

Hardware interlocks, such as door switches, normally prevent motors frombeing powered when an operator is within the workspace of the machinerysubject to control, such as a robot. However, when teaching a systemcomponent, that is when the component is in teach mode, the normalhardware interlocks may be bypassed to allow an operator to enter theworkspace of the robot. In many instances, a teach pendant used todirect the robot has a “live-man” switch that removes power to the robotin the event that pressure is not applied to the switch. According tothe disclosed embodiments, the master controller 105 or clustercontroller 110 may also provide commands that ensure that the speed andforce of the robot are kept within acceptable limits specified toaccommodate a human presence in the workspace.

The control system 100 may incorporate several features to accommodatethe human presence. Referring to FIGS. 1(1 a-1 b), during general systemoperations, the master controller 105 may generate motion profiles forindividual axes 125. In the example of FIG. 12, several axes may begrouped together as part of a robot 1210, and the master controller 1245may generate a series of PVT frames for each axis controlled by theremote controllers 1230, 1235, 1240 so that the end effector 1220executes a particular trajectory. It should be noted that although theend effector may be moving at a constant velocity, the velocity of thedifferent axes that make up the robot 1210 may vary with position andtime. Thus the velocity parameter of the PVT frames may vary withrespect to position and time due to the robot kinematics. When anoperator is present in the work cell 1200 the system may use velocitylimiting techniques to protect the operator. In effect, the system maygenerate trajectories such that the resultant end effector motionprofile is within a required speed limit. This may be accomplished bycalculating the trajectory as described above for the robot whilesetting the velocity parameter of the PVT frames for axes controlled byremote controllers 1230, 1235, 1240 to a position- and time-dependentnot-to-exceed limit.

Likewise, although the end effector may be exhibiting a constant forcein a particular direction, the torque of the different axes that make upthe robot 1210 may vary with position and time. A position- andtime-dependent torque limit may also be imposed when an operator ispresent in the work cell 1200 such that the resulting force of the endeffector remains below a particular limit by adding a term to the framessent to the cluster controller 1215 which manages remote controllers1230, 1235, 1240. In a particular position of the robot 1210 there is aunique relation between the torques applied by the motors at the axislevel and the force produced by the end-effector. Consequently, it ispossible to use the model of the robot to calculate the maximum motortorques such that the corresponding force produced by the end-effector1220 cannot exceed a maximum allowable value. These maximum torques maybe calculated every time when a new set of PVT or PVT-FG frames for axescontrolled by remote controllers 1230, 1235, 1240 is generated and sentto the cluster controller 1215.

It is a feature of the present embodiments to utilize unique messageframes, referred to as PVT LIMIT frames, in the teach mode of operation.The PVT LIMIT frames may be similar to those shown in FIGS. 6 and 7above, however, their velocity term is calculated so as not to exceed aparticular limit and they include an optional torque limit term.

FIG. 26 shows an exemplary PVT LIMIT frame 2600 with a torque limitterm. The PVT LIMIT frame 2600 includes position data 2610, velocitydata 2615, and time data 2620. In one embodiment the data is in binaryformat grouped together in one or more bytes. In another embodiment eachof the position data 2610, velocity data 2615, and time data 2620occupies four bytes. PVT LIMIT frame 2600 may optionally include headerinformation 2625 and trailing information 2630, both of which mayinclude synchronizing, identification, parity, error correction, orother types of data.

As a feature of the disclosed embodiments, PVT LIMIT frame 2600 includesa torque limit term 2635 that specifies a not to exceed torque limit.PVT LIMIT frame 2600 may also include additional data of varying lengthsor amounts between or among the header, position, velocity, time, andtrailing data. PVT LIMIT frame 2600 may optionally include another datafield 2640 for any other suitable data. It should be noted that whileFIG. 26 shows the various information or data in specific locations orareas of the frame, the different types of information and data may belocated anywhere within the PVT LIMIT frame 2600. It should also benoted that the PVT LIMIT frame 2600 is not limited to any particularlength.

FIG. 27 shows an exemplary PVT-FG LIMIT frame 2700 with an optionaltorque limit term. PVT-FG LIMIT frame 2700 includes optional headerinformation 2710, position information 2715, velocity information 2720,time information 2725, and optional trailing information 2730.

In addition, PVT-FG LIMIT frame 705 includes at least one feedforwardterm 2735 and at least one gain term 2740. The data may be in binaryformat grouped together in one or more bytes. In one embodiment ofPVT-FG LIMIT frame 705 the position 2715, velocity 2720, time 2725,feedforward 2735, and gain 2740 terms each occupy four bytes. Similar toPVT LIMIT frame 2600, PVT (FG) LIMIT frame 2700 may include other dataof varying lengths or amounts, distributed among or between the variousterms.

Similar to PVT frame 2600, the disclosed embodiments include a torquelimit term 2745 as part of PVT-FG LIMIT frame 2700 that specifies a notto exceed torque limit. PVT LIMIT frame 2700 may also include additionaldata of varying lengths or amounts between or among the header,position, velocity, time, and trailing data. Another data field 2750 maybe included for any other suitable data. It should be noted that whileFIG. 27 shows the various information or data in specific locations orareas of the frame, the different types of information and data may belocated anywhere within the PVT-FG LIMIT frame 2700. It should also benoted that the PVT-FG LIMIT frame 2700 is not limited to any particularlength.

As mentioned above, the velocity and torque limit terms may becalculated to impose an overall limit on the speed and force of the endeffector 1220 (FIG. 12). The trajectory is calculated for the endeffector so that its velocity does not exceed the specified limit. Theresulting position, velocity and acceleration profiles are thenconverted to positions, velocities and accelerations of individual axesusing the inverse kinematic equations of the robot described above. Thetrajectory information is converted to PVT LIMIT or PVT-FG LIMIT framesand sent to cluster controller 1215 which manages remote controllers1230, 1235, 1240.

It should be understood that the master controller may send PVT LIMIT orPVT-FG LIMIT frames also to autonomous remote controllers, for instance,if some or all of robot axes are controlled by autonomous remotecontrollers rather than by remote controllers subordinated to a clustercontroller.

As one aspect of the disclosed embodiments, during the teach mode ofoperation, the cluster controller 1215, which manages remote controllers1230, 1235, 1240, or generally an autonomous remote controller, whichcontrols some or all of robot axes, may operate to crosscheck thetrajectory data sent by the master controller 1245. Thus, when thecontroller receives a PVT LIMIT frame, the controller may operate toverify the applicability of the message and its data by performing anumber of crosschecks including checking for a maximum velocity, avelocity tracking window, velocity debounce time, a maximum torque, anda maximum torque debounce time.

To check for a maximum velocity, the controller may recognize that theaxis is in teach mode and also identify a maximum velocity limit for theaxis. Upon receiving a frame, the controller verifies that the velocityterm is below the maximum velocity specified for the axis in teach mode.In the event that the maximum velocity is exceeded, the remotecontroller may send an alert to the master controller.

The controller may also determine a velocity tracking window, that is, amaximum value for the difference between a commanded velocity from aframe message and an actual measured velocity, such as measured by anencoder for the axis. In the event that the velocity tracking window isexceeded the remote controller may send an alert as above. In sometransient conditions, the velocity tracking window may be exceeded forbrief periods of time without an alert being issued. However, this timeperiod may also be specified and monitored, and if the velocity trackingwindow is exceeded for this specified time, the controller may alsoissue an alert.

As mentioned above, a maximum torque allowed for an axis may bedetermined during a trajectory execution, especially in teach mode. Thecontroller may check the torque commanded by the control loop againstthe maximum torque specified by the limit terms of the PVT LIMIT orPVT-FG LIMIT frames received, and may generate an alert if the maximumtorque specified by the frames is exceeded. As with the maximumvelocity, the maximum torque may be exceeded for brief periods of timewithout an alert being issued. However, this time period may also bespecified and monitored, and if the maximum torque is exceeded for thisspecified time, the controller may also issue an alert. The controllermay recognize that the axis is in teach mode and also identify arelevant global maximum on the not-to-exceed torque limit it expects toreceive in the frames. If this global maximum is exceeded, thecontroller may also issue an alert.

In addition to an alert, a failure of any of these parameters may alsocause the controller to disable the motor driver output stage in orderto stop any motion. The master controller may be alerted and may alsostop all motion on all other associated axes.

Referring again to FIG. 12, another aspect of the disclosed embodimentsused to accommodate a human presence in the workspace may includeperiodic verification that the communications network, the clustercontroller and the master controller are functional. The remotecontrollers 1230 1235, 1240 may be programmed to monitor communicationssuch that if a message is not received periodically the remotecontroller may stop motion for its axis.

For example, the remote controllers 1230, 1235, 1240 may be programmedto monitor the time period between message transmissions, such asreceiving torque commands. As another example, an autonomous remotecontroller may monitor the time period between PVT frames. If a torquecommand or PVT frame does not arrive within the expected period, theremote controller or autonomous remote may consider the communicationnetwork 1250, the cluster controller 1215 or the master controller 1245as not being functional and may proceed to stop motion on the axis oraxes under its control. The periodic message monitored by the remotecontroller or autonomous remote controller may also be the cycle startmessage used to synchronize the clocks of these controllers.

The master controller 1245 may also monitor network communications bymonitoring receipt of periodic status messages. Upon failure to receivea status message from the cluster controller 1215, or any of the remotecontrollers 1230, 1235, 1240, the master controller 1245 may attempt tostop all motion on any of the axes associated with the clustercontroller 1215 and controlled by the remote controllers 1230, 1235,1240.

The aspects of crosschecking the trajectory data, verification of thecommunications network, master controller, and remote controllers may beaccomplished by hardware specifically for that purpose at each networknode. For example, the cluster controller 1215, remote controllers 1230,1235, 1240, or an autonomous remote controller may include dedicatedcircuitry that operates independently to perform any of thecrosschecking functions described above for the trajectory data sent bythe master controller 1245. As another example, one or more of themaster controller 1245, the cluster controller 1215, remote controllers1230, 1235, 1240, or an autonomous remote controller may each includededicated circuitry for monitoring the time between messages or thereceipt of periodic messages.

FIG. 28 shows a block diagram of an exemplary integrity monitor 2800that includes dedicated circuitry specifically for monitoring systemintegrity. The integrity monitor 2800 may include a processor 2810, asemiconductor memory device 2815, non-semiconductor memory 2820, and aninterface 2825 to the communications network 120. The integrity monitor2800 may also include axis encoder sensing circuitry 2830 for receivingaxis position information signals 2835, and axis motor current sensingcircuitry 2840 for receiving signals indicating an axis motor currentdraw 2845. In addition, the integrity monitor may also include a timer2850, inputs for sensing that the teach mode is being employed (Teach,2855) and any immediate stop requirements (I-Stop, 2860), and a switchinterface 2865 to control power for the axis.

Generally, the processor 2810 operates under control of programs storedin memory 2815 to crosscheck trajectory velocity and torque data, verifythe operation of the communications network 120, identify when aparticular axis has exceeded its operating parameters, and remove powerfrom the axis when required.

The processor 2810 may sense that the axis is in teach mode and mayidentify the maximum velocity limit for the axis using the velocity termin the PVT frames received. The processor 2810 may then operate toverify that the actual velocity of the axis term in the frames receiveddoes not exceed this maximum velocity specified for the axis in teachmode limit. The processor 2810 may also determine the velocity trackingwindow, if it has been exceeded and for how long. The processor 2810 mayalso determine the maximum torque allowed, if it has been exceeded, andfor how long. In the event of a failure of any parameters, the processor2880 may control the shutdown of the axis and coordinate with othercontrollers that may also be brining their axes to a controlled stop.

The processor 2810 may also monitor the time period between messagetransmissions, such as receiving PVT frames, and may issue an alert orbegin a controlled shutdown if a PVT frame does not arrive within theexpected period. Optionally the integrity monitor 2800 may communicatewith other integrity monitors through a dedicated network 2870.

The European machinery directive (EN 60204-1) defines two categories ofan immediate stop. The first, Category 0, is defined, as an“uncontrolled shutdown”, in which power is simply removed. The secondcategory, Category 1, is defined as a “controlled shutdown”, where poweris maintained long enough to bring motion to a stop before beingremoved. It is highly desirable for the components of the control systemto comply to a category 1 stop, for accommodating a human presence andto prevent product damage.

In the event of a power loss, it may be important to control the motionof the axes of the system so that the axes come to a stop withoutcausing damage to equipment and material or endangering an operator. Onemethod commonly used is to short the windings of an axis motor through aresistor when a power loss arises. However, this requires careful tuningof resistance values to match the motor winding parameters to get thedesired decelerations, and may not be acceptable for robots that executecoordinated motions since substantial tracking errors and subsequentdamage to equipment or material may occur if shutdown of the individualaxes is not coordinated.

Another common practice is to include an uninterruptible power supply(UPS). While this solution provides the power necessary to bring axes toa stop in a coordinated fashion, it may add substantial cost, size andweight, and may require periodic service.

Another method includes providing capacitance or battery backup to theoutputs of the power supplies to provide enough power to allow theremote controllers or autonomous remote controllers to bring theirassociated axes to a controlled stop. This may require substantialcapacitance or battery capacity, however, because the power shouldremain relatively stable during the entire deceleration event.

One method utilized in the present control system may be based onrectification of the incoming AC voltage (220V in the exemplary case)through Power Factor Correction (PFC) circuitry with capacitanceprovided at the DC output of the PFC circuitry. The resulting DC voltagemay be fed into a wide input range DC power supply (48V in the exemplarycase). When power is lost, the capacitor keeps the DC power supplyrunning despite a substantial decay in the input voltage.

The energy stored by the capacitance should be sufficient to allow themotion controller to plan and execute a trajectory that brings therobot's end-effector from its current velocity to zero velocity at apredefined deceleration rate specified to protect the equipment andmaterial, and thus bring the robot to a controlled stop whilemaintaining coordinated motion along a specified trajectory, withoutdamage and without losing the axes positional information.

Another embodiment may include a capacitive storage module 3300 as shownin FIG. 33. The exemplary capacitive storage module may provide thenecessary power to allow category 1 operation even during power outagesand brownouts. Because of a unique design, the module may alsofacilitate the use of commercial off the shelf (COTS) PFC power suppliesthat may not comply to certain brownout requirements, for example,European Union or Semi F-47 voltage sag tests.

The components of the capacitive storage module 3300 may be mounted on asingle printed circuit board. An AC voltage 3335 may be rectified bybridge 3305 and the rectified voltage output 3307 may be passed directlyto the Power-Factor-Corrected power supply. In parallel with therectified voltage output 3307, a charging circuit 3310 may charge andmaintain a high voltage on a capacitive storage bank 3315. A powersupply supervisor circuit 3320 may be connected in parallel with thecapacitive storage bank 3315.

The power supply supervisor circuit 3320 may include a processor,memory, program storage, and various sensors and monitoring circuitry.The program storage may include programs accessed by the processor thatdirect the operations of the power supply supervisor, includingmonitoring output voltage 3307, operating switch 3325, monitoring thestorage capacity and voltage of capacitive storage bank 3315, andmonitoring the input voltage 3335.

The power supply supervisor 3320 may monitor the rectified voltageoutput 3307, either through a direct connection or by other mechanisms.When the power supply supervisor circuit 3320 determines that therectified voltage output 3307 fails to meet a predetermined criteria,for example, as a result of a power loss, the power supply supervisorcircuit 3320 connects the capacitive storage bank 3315 to the rectifiedvoltage output 3307 through switch 3325.

Several advantages may be attained by this design. Firstly, thecapacitors in the capacitive storage bank may be sized to provide only asmall percentage more than the total power required for the decelerationevent. Secondly, output voltage may be precisely maintained while thecapacitors discharge approximately 85% of their stored energy since COTSPFC power supplies may generally operate over a wide input voltagerange. Thirdly, energy storage at higher voltage makes this solutionmore compact and less expensive because energy stored in a capacitor isproportional to the product of capacitance and voltage squared, and thephysical size of a capacitor is approximately proportional to theproduct of capacitance and voltage.

In another implementation, the power supply supervisor 3320 may providethe warning signal 3330 to external circuitry, for example, circuitryfor monitoring system integrity, a power control function, or the mastercontroller 105. The warning signal may be used to alert other networkcomponents of possible power problems and for other purposes, forexample, to allow for a category 1 stop as defined by EN 60204-1. Thecontrol system may also use this warning signal 3330 to confirm that thecapacitive storage bank 3315 is fully charged before initializingmotion. The warning signal 3330 and the capacitive storage bank 3315 maytypically be enabled concurrently, allowing the control system 100 toutilize the stored energy in the capacitor storage bank 3315 to bringany moving axes to rest. The energy stored may generally be equal to orgreater than the energy required to bring the system to rest regardlessof the state of the system. For example, the stored energy may includeenough energy to bring the system to rest when all axes are moving atmaximum velocity.

Alternatively, the timing of the warning signal 3330 may be shifted withrespect to the engagement of the capacitive storage bank 3315 so thattemporary input power abnormalities do not cause unnecessary disruptionsin service. This is a particularly attractive method of implementationbecause it allows the use of power supplies that may not meet brownoutrequirements.

The warning signal may also provide information regarding energy storagecapacity, input voltage, capacitor bank voltage, and input power qualitywhich may be used for predictive and automatic failure detection.

It is another feature of the present embodiments to utilize monitored,redundant, solid state logic to detect and react to inputs which requirethe removal of axis power. This provides the flexibility to support anarchitecture in which immediate stop information can be shared acrossmultiple zones as will be described below.

A power control function 4000 for implementing this feature is shown inFIG. 40. The power control function includes circuitry for detectingimmediate stop inputs 4005, one or more timers 4010, and variousprocessors, memories, and support circuitry for carrying out the powercontrol function. The power control function provides signals indicatingthat it has initiated power removal (Stop, 4035), control signals 4040for one or more robotic logic power supplies 4055, and control signals4045 for one or more relays 4060 controlling robotic motor powersupplies 4065. The immediate stop detection circuitry 4005 receivesinputs from various interlocks 4015, immediate stop signals 4020,liveman signals 4025, and teach mode signals 4030 from various controlsystem components, and also receives motor power enable signals 4070from the master controller 105 and monitor signals 4050 from the relays4060. The liveman signals 4025 indicate that there is a human present inat least one robotic workspace of the control system 100. The teach modesignals 4030 indicate that at least one component of the system is beingtaught an operation.

While the power control function is described as including varioushardware components it should be understood that the power controlfunction may be implemented in hardware, software, or any combination ofhardware and software.

When the master controller 105 requests that motor power be enabled, thepower control function 4000 first verifies the state of all immediatestop 4020, liveman 4025, interlock 4015, and teach mode 4030 signals.The power control function 4000 also confirms that the contactors ofrelay 4060 are in the appropriate state and are not welded and may alsoverify that any solid state switches associated with the relay are notconducting. If the state of each of the immediate stop, liveman,interlock, teach mode signals, contactors, and switches meets allnecessary requirements, the relay 4060 is enabled. It should beunderstood that the relay 4060 may also be implemented as one or moresolid state switching device.

When any of the immediate stop, liveman, interlock, or teach modesignals reaches a state that requires the removal of motor power, thepower control function alerts the master controller 105 and starts thetimer 4010. The timer 4010 is programmed to allow adequate time for thesystem component generating the signal requiring power removal to cometo a controlled stop. The duration of the timer 4010 may be determinedby the system component mode of operation. For example, the timer may beset at different intervals for a robot traveling at different speeds, orin teach mode.

Upon expiration of the timer 4010, the power control function 4000disables the motor power supply through relay control signal 4045. Motorpower may only be re-applied when all of the immediate stop, liveman,interlock, or teach mode signals return to a state that allowsresumption of motor power, and the motor power enable signal 4070 isreasserted.

The power control function 4000 may typically resides in a powerdistribution unit. It may serve groups of remote controllers andautonomous remote controllers, for instance, when incorporated intopower distribution units of individual zones of the control system asdescribed below. The power control function 4000 may also be implementedas a pluggable daughter card or module that may be reused in differentpower distribution units designed for specific applications.

FIG. 41 shows another embodiment of the power control function 4100where the immediate stop detection circuit includes circuitry forsensing the warning signal 3330 from the power supply supervisor 3320 ofthe capacitive storage module 3300 discussed above. The warning signal3330 may be used in a manner similar to the immediate stop, lineman,interlock, or teach mode signals to trigger power removal from one ormore network components.

In a production environment where any failure and subsequent downtimecan mean tens of thousands of dollars in damaged material and lostproductivity, the reliability of a motion control system is a criticalrequirement. The architecture of the control system 100 (FIG. 1,1 a-1 b)of the disclosed embodiments may generally achieve better reliability bylocating remote controllers close to the components subject to control,thus reducing the length and complexity of wires and harnesses whichcarry feedback and action signals. However, in some instances thecommunication network 120 itself may be vulnerable to failures since itmay run relatively long distances and, in many cases, may remain fullyoperational only if all of the nodes and connections between them arefunctional. Otherwise said, in many topologies, a malfunction of asingle connection or a single node may cause a segment or the entirecommunication network 120 to fail. Therefore, it is desirable to providea communication network solution which will keep the control system 100operational to the maximum extent possible even in the case of a faultycommunication network connection, such as a cable break, or a failure ofone or more of the network nodes.

The IEEE 1394b standard and other network standards and implementationsmay allow for inactive segments that form physical loops in an otherwisetree type network topology. The inactive segments may be used to provideredundant connections between nodes of the communication network 120.The network may be enabled to automatically disable the redundantconnections, for example, by selective disabling of PHY ports. Upon afailure, the network may have the capability to selectively enable theredundant connections to form a path to nodes isolated by the failure.This may be accomplished, for example, by using the facilities inherentin the IEEE 1394b standard. Other network implementations may also havethe capability of detecting and disabling redundant connections and thenselectively enabling them in the event of a failure.

These features may be leveraged to offer a unique self-healing faulttolerance that guarantees that the control system 100 will operate evenif there is a cable break or a complete failure of a node on thecommunication network 120. In particular, if a network node or an activenetwork connection fails, the communication network 120 may reconfigureitself to route communications through a redundant connection that wasnot active before the failure. A connection between two network nodeswill be referred to as a segment.

It is important to note that while the IEEE 1349 standard is used as anexample when describing the disclosed embodiments, the disclosedembodiments are not limited to IEEE 1394 based networks. Other networkimplementations may also be utilized so long as they include featuressuitable for practicing the disclosed embodiments.

If a node on the network 120 fails, the network may reconfigure itselfto route the communication through alternate segments, and may performan immediate stop of all or selected axes of motion using the newcommunication routes. Thus, the physical loops in the bus topology mayprovide redundant communication paths through the entire network, whichcan be used as secondary data channels in the event of a failure.

FIG. 34 a shows an exemplary topology 3400 of network 120 that providesredundant connections. Topology 3400 includes a main loop 2305 and anumber of peripheral loops 3410, 3415, 3420. The main loop 3405 includesa master controller 3425 and each of the main loop 3405 and peripheralloops 3410, 3415, 3420 include remote controllers 3430. Note that theactive segments 3470 of topology 3400 form a tree type topology whilethe inactive segments 3475 provide redundant loop connections betweenthe nodes.

FIG. 34 b shows the topology 3400 with a fault 3435 in a segment 3440 ofthe main loop 3405. As described above, the network 120 has disabled thenow unused segment 3440 at the faulty node 3435 and has reconfigureditself to route communications through previously unused segment 3445.FIG. 34 c shows the topology 3400 with a faulty node 3450, for example afaulty remote controller, in the main loop 3405. In this example, thenetwork 120 has disabled segments 3455, 3460 and now routescommunications through previously unused segment 3465. FIGS. 34 d and 34e show similar exemplary failures and reconfiguration techniques inperipheral loop 3420.

In a simple ring topology, it may be relatively easy to identify afailure and switch to a redundant connection. However, it may besubstantially more difficult to enable such a self-organizing andself-healing functionality in a general system with multiple physicalloops. The present embodiments offer a mechanism that utilizes theframework of any network implementation capable of utilizing redundantconnections to compensate for failures to permit a control system withmultiple physical loops in the communication network 120 to continue tofunction even as its configuration changes over time due to failures ofsegments or nodes.

The mechanism according to the present embodiments may also include amethod for efficient buffering of trajectory frames, and a method forcompensation for synchronization delays in the communication network.

Motion synchronization may be maintained in the clustered architecturecontrol system 100 by synchronizing the clocks on all network nodes,including the master controller 105, cluster controllers 110, and remoteand autonomous remote controllers 115. In one implementation, asynchronization message, also referred to as a cycle start message, maybe sent by a node designated as a cycle master, which is typically themaster controller 105.

The delay in receiving the synchronization message from the mastercontroller 105 by a network node causes differences among clocks in thenetwork nodes. The largest component of the delay is associated withrepeater delays during the transmission of the synchronization message.Repeater delays refer to delays introduced by each node during theprocess of receiving the message and sending the message on to the nextnode until the message arrives at its destination. The total propagationdelay for a given node may be assumed to be a cumulative sum of allrepeater delays along the path from the master controller to thedestination node.

The path of a cycle start message may be determined for each node fromthe network topology. The propagation delay may be estimated based onthe message path. The estimated propagation delay for each node may beoffset by adjusting the trajectory data in the PVT frames for that node.

In one approach for estimating the propagation delays, the mastercontroller 105 may simply use a nominal value of 144 ns, based on theassumption that the network topology is designed so that the greatestpropagation delay does not exceed 144 ns. In another approach, therepeater delay for each node may be predetermined and stored in a memorylocation, for example, within the node. The master controller may readthe repeater delay for a particular node from the memory location. Inone example, the repeater delay may be stored and read from a delayfield in a node register, for example, a base PHY register.

The master controller 105 may then utilize the repeater delays tocalculate a delay compensation for each node. In one embodiment, themaster controller 105 may index the repeater delays by an ExtendedUnique Identifier (EUI-64) for nodes that report a EUI-64, and may useestimated values for nodes that do not.

Another method for estimating the total propagation delay from themaster controller 105 to any of the nodes on the communications network120 is for the master controller 105 to ping each node and record theresponse time to the ping. Alternately, the master controller may recordthe response to a PHY register request packet. The difference in theround-trip times for the ping or the request and response may beutilized as the cumulative propagation delay from the master controllerto the different nodes on the communication network 120.

The delay compensation for each node may be recalculated by the mastercontroller each time the communication network reconfigures itself.

FIG. 38 shows a result of a typical IEEE 1394b self-identificationprocess. It is important to note that other network implementations mayalso be capable of such self-identification and that the disclosedembodiments are not limited to IEEE 1394b type networks.

Assuming that the path for node M₀ to the master (root) is defined bynodes M₀, M₁, M₂, . . . , M_(n), where M_(i) are PHY id's and M_(n) isthe root (M₀<M1<M2< . . . <M_(n)), and denoting p(M_(i)) as the parentof M_(i) and the repeater delay for M_(i) as t(M_(i)), the totalpropagation delay for node M₀ is Σt(p(M_(i))), where i=0, 1, 2, . . . ,n−2.

The master controller 105 can be made aware of reconfiguration events byobserving bus-reset and selfid-complete messages occurring on thecommunication network 120. The selfid-complete packets may provideenough information so that the master controller 105 may determine thenew network topology and the paths from the master controller to eachnode. The path from each node to the master controller 105 may beuniquely defined by the concatenation of paths from any node to itsparent node until the root is reached. The total propagation delay fromeach node may be determined from a sum of the repeater delays along thatpath. Once the total propagation delay for a node has been determined,the node may use the propagation delay information to offset trajectorydata (PVT frames).

Referring to FIG. 35, the following procedure would be advantageous inrecalculating propagation delays when the communication network 120reconfigures as a result of a segment or node failure.

As shown in block 3505, the master controller 105 may generally obtain acycle master role in the communication network 120 and, as shown inblock 3510 may estimate the repeater delays for each node on thecommunication network 120 as described above. As shown in block 3515,the master controller sends the corresponding delay estimate to eachnode on the communication network 120. Each remote node on thecommunication network 120 applies the estimate received from the mastercontroller 105 as a time offset when executing PVT frames as shown inblock 3520. For instance, the time for execution of a given PVT framecan be calculated as the time field of the PVT frame minus the estimateof the propagation delay.

In another embodiment, the PVT or PVT-FG frames send by the mastercontroller 105 may include an additional field called TIME_OFFSET whichcarries the propagation delay information.

Each network node may then apply the propagation delay information fromthe TIME_OFFSET field when executing PVT frames. For instance, the timefor execution of a given PVT frame can be calculated as the time fieldof the PVT frame minus TIME_OFFSET.

In case of a topology change accompanied by a bus reset event, theremote node may discard the TIME_OFFSET field in the PVT frames thatwere buffered before the bus reset and are to be executed using theresynchronized clock after the bus reset, and may substitute the fieldwith TIME_OFFSET information from the first PVT frame received after thebus reset.

FIG. 36 shows an exemplary PVT frame 3605 with an additional TIME_OFFSETfield. The PVT frame 3605 includes position data 3610, velocity data3615, and time data 3620. PVT frame 3605 may optionally include headerinformation 3625 and trailing information 3630, both of which mayinclude synchronizing, identification, parity, error correction, orother types of data. In addition, PVT frame 3605 may include aTIME_OFFSET field 3635 which includes propagation delay information forthe node to which the frame is addressed.

It should be noted that while FIG. 36 shows the various information ordata in specific locations or areas of the frame, the different types ofinformation and data may be located anywhere within the PVT frame 3605.It should also be noted that the PVT frame 3605 is not limited to anyparticular length.

FIG. 37 shows an exemplary PVT-FG frame 3705 with an additionalTIME_OFFSET field. PVT-FG frame 3705 includes optional header 3710position 3715, velocity 3720, time 3725, and optional trailinginformation 3730, similar to PVT frame 3605. In addition, PVT frame 3705may include a TIME_OFFSET field 3735 which includes propagation delayinformation for the node to which the frame is addressed.

Similar to PVT frame 3605, PVT-FG frame 3705 may include other data e.g.3740 of varying lengths or amounts, distributed among or between thevarious terms.

As yet another approach, the propagation delays may be estimateddirectly on the network node. Each network node may determine the pathfrom the master controller 105 based on the information in the self-idpackets following a bus reset. Each node may then calculate an estimateddelay essentially equal to the propagation delay, and apply thecorresponding offset when executing PVT frames.

In the control system 100 events may occur that require one or morecomponents to stop immediately, or to invoke some of the velocitylimiting or force limiting features described above. These situationsmight adversely impact other components that interact with the affectedcomponent, and in some cases might unfavorably influence the entirecontrol system.

It is a feature of the disclosed embodiments to divide the controlsystem 100 into zones so that events requiring component stop, velocitylimiting, or force limiting occurring in one zone may not affect theoperation of the other zones. Another advantage of segregating thesystem into zones is that components or nodes of the control system 100may be serviced, for example, in teach mode, or shut down with powerremoved, while other components or nodes continue to function.

A control system with multiple work zones may provides a globalimmediate stop functionality across all of the zones, and locally handleinterlocks in each zone to provide access to selected zones whilemaintaining operations in other zones. Teach pendant and livemanfunctionality may also supported on a per-zone basis. Each zone may alsohave its own power distribution unit with integrated safety support.

An example application of a control system with multiple zones accordingto the disclosed embodiments is shown in FIG. 39(39 a-39 c).

FIG. 39(39 a-39 c) shows a portion of control system 100 having anatmospheric zone 3905 and a vacuum zone 3910. The atmospheric zone 3905includes two robots 3906, 3907 and two aligners 3909, 3908. Vacuum zone3910 includes a robot 3911. Each zone may have an associated intelligentpower distribution unit 3915, 3920 which may include a power controlfunction 4000 as described above. Local system integrity signals 3930are used to communicate I-stop, interlock or liveman events to themaster controller 105 for initiating a controlled stop either globallyor within a single zone. In this particular example, the local systemintegrity signals 3030 are fed to one a remote controller 3940, 3945within each zone and communicated to the master controller 105. Themaster controller communicates to the components in each zone throughthe communication network 120.

In addition, a general communication network 3950, for example, anEthernet network, may generally serve to accommodate communication ofthe control system with other subordinated or independent automationcomponents, such as loadports in semiconductor substrate-handlingapplications, including communication with one or multiple teachpendants 3955, 3960. A teach pendant interface provides communication tothe general communication network 3950, and may also include I-stop,lineman and pendant presence signals.

Each zone 3905, 3910 shares zone to zone integrity signals 3925 thatinclude signals for interlocks, immediate stop indications, and thestatus of system AC power. A previous zone and next zone signal may beincluded that indicates the presence of adjacent zones.

The master controller operates to isolate motion in the zones 3905, 3910so that events occurring in the atmospheric zone 3905 do not effect theoperation of actions in the vacuum zone 3910. For example, in the eventof a failure in the atmospheric zone 3905, the atmospheric zone may bedisabled and brought to a controlled stop. While the embodiments serveto isolate the actions in one zone from another, they also provide theability to communicate events among the zones and to the mastercontroller that may warrant a coordinated controlled shutdown of morethat one zone.

For example, the master controller may identify a zone to zone immediatestop signal as requiring a shut down of the atmospheric zone 3905. Themaster controller 105 may also shut down vacuum zone 3910 because itreceives material from the atmospheric zone 3905. Alternately, themaster controller may route work originally scheduled for theatmospheric zone 3905 to another zone in the control system 100.

Thus, the disclosed embodiments provide a method of maintaining theintegrity of a control system network by assigning nodes of the networkinto zones such that motion in a first zone is isolated from motion inzones other than the first zone.

It has been observed that if some robots are stationary for a period oftime they may have positional errors upon restarting. For example, uponstartup after idle, the robot may not proceed to a proper location orplace a substrate at a proper location within an acceptable operationaltolerance. These errors may be due to the temperatures and relativelocations of various components, lubricant viscosity, or any number ofother factors. These errors are generally eliminated after a number ofmovements.

It is a feature of the disclosed embodiments to record the amount oftime a robot is idle. If a certain idle time has been exceeded,performance characteristics of the robot may be determined. If theperformance characteristics do not meet specifications, the robot may bedirected to perform a warm up exercise. The warm up exercise may includeone or more motions that provide enough movement to eliminate positionalaccuracy errors that surface as a result of the robot being idle.

In another aspect of the disclosed embodiments, if the idle time hasbeen exceeded, the robot may be directed to perform the warm up exercisewithout determining the performance characteristics.

FIG. 29 shows a work cell 2900 in which this embodiment may beimplemented. Work cell 2900 includes a robot 2910 with a clustercontroller 2915 and three remote controllers 2930, 2935, 2940. Thecluster controller 2915 communicates with a master controller 2945through a communications network 2950. The work cell 2900 may alsoinclude an aligner 2955 which may be controlled by a remote controller2960. The remote controller 2960 may be controlled by the mastercontroller 2945. The work cell 2900 may optionally include one or moresensors 2960, 2965, 2970 that sense the position of the robot. In oneembodiment, the sensors 2960, 2965, 2970 may be mounted on or otherwiseincorporated into robot 2910. In an exemplary embodiment, the work cell2900 may be part of the clustered architecture control system 100 (FIG.1,1 a-1 b).

Referring back to FIG. 3, cluster controller 2915 generally includes aprocessor 305, read only memory 310, random access memory 315, programstorage 320, and a network interface 330 to network 120. Processor 305is generally operable to read information and programs from a computerprogram product, for example, a computer useable medium, such as onboard programmable memory 335, read only memory 310, random accessmemory 315, and program storage 320.

On board programmable memory 335, read only memory 310, random accessmemory 315, and program storage 320 may include programs for determiningperformance characteristics of robot 2910 and for directing robot 2910through the motions of the warm up exercise.

Exemplary operations of the disclosed embodiments will now be describedwhile referring to FIGS. 29 and 30.

While the functions associated with determining a robot idle time, robotperformance characteristics, and implementing a robot warm up exerciseare described primarily as being performed by the cluster controller2915, it should be understood that the functions may be performed by themaster controller 2945, a remote controller 2930, 2935, 2940, anysuitable component of the work cell 2900, or any suitable component ofthe clustered architecture control system 100 (FIG. 1,1 a-1 b) when thework cell 2900 is part of such a system.

Furthermore, while the idle time, performance characteristics, and warmup exercise are generally associated with the robot 2910, the functionsassociated with determining these functions and characteristics may alsobe implemented for individual axes or joints of a robot, othercomponents of the work cell 2900, or for other clustered architecturecontrol system components.

The cluster controller 2915 may be equipped with circuitry or programsthat recognize when the robot 2910 is in an idle state. For example, therobot 2910 may receive an express command to enter a stand by mode, toshut down, or simply may not receive any motion commands for a certaintime. As shown in block 3010, the cluster controller 2915 determinesthat the robot 2910 is idle, and as shown in block 3015 saves a timestamp as an indication of the time that the idle state was determined.

The cluster controller 2915 monitors commands sent to the robot 2910 asshown in block 3020. If a motion command is received, the clustercontroller 2915 retrieves the time stamp and determines how long therobot has been idle as shown in block 3025. As shown in block 3030, ifan idle time threshold has been exceeded, the cluster controller maythen issue a warm up exercise to the robot 2910 in the form of forexample, one or more motion commands that generally provide enoughmovement to eliminate positional accuracy errors due to the robot beingidle, as shown in block 3035. After executing the warm up exercise, therobot may then execute the motion command, as shown in block 3045.

FIG. 31 shows an alternate procedure for block 3035 of FIG. 30. As shownin block 3110, if the idle time threshold has been exceeded, the clustercontroller 2915 may check the performance characteristics of the robot2910. For example, the cluster controller 2915 may issue a test motioncommand to the robot and then may check sensors 2960, 2965, 2970 toensure that the robot executed the command within specifications. Asanother example, the cluster controller may check the performancecharacteristics by instructing the robot 2910 to place a substrate 2975on aligner 2955 and then checking the alignment of the placed substrate.

If the performance characteristics are within specification, the clustercontroller 2915 may allow the robot to execute the motion command, asshown in block 3045 of FIG. 31. If the specifications are not met, thecluster controller 2915 may issue an alert to an operator or a requestto assist, for example through user interface 225 (FIG. 2), requestingan override, as shown in block 3115. As another alternative, the clustercontroller 2915 may stop the operation of the robot 2910 until a userintervenes. Once an override has been provided, the robot may thenexecute the motion command as shown in block 3045 of FIG. 31.

It can be seen that the disclosed embodiments provide a mechanism forcompensating for robot placement errors by executing a warm up exercise.In one aspect of the embodiments, the warm up procedure may be performedif the robot has been idle for a certain period of time. As a furtherrefinement, the performance characteristics of the robot may bedetermined and the warm up exercise may be performed if certainspecifications are not met. The warm up exercise may include one or moremotions that provide enough movement to eliminate positional accuracyerrors that surface as a result of the robot being idle.

In a complex control system it may be advantageous to utilize astandardized set of interface conventions for accessing the systemcomponents. These may be provided by an application program interface(API) that may include a set of commands, parameters, variables, etc.that provide a user with a common form for communicating with varioussystem components.

It is a feature of the disclosed embodiments to provide an API thatincludes a generalized command set that allows the use of a generalcommand to perform an operation and specific arguments to identifyparticular components, locations, and other parameters for performingthe operation.

It is another feature of the disclosed embodiments that, through theAPI, the actual motions to accomplish the operation may vary dependingon the arguments. For example, using a “PickFrom” command specifying arobot and an aligner as the location may result in an entirely differentset of movements than specifying a robot and a loadport as the location.

Referring to FIG. 42(42 a-42 c), the API may include a number of objectsincluding a resource coordinator 4305, a sequence recipe 4310, and asequence manager 4315. Commands from the resource coordinator 4305 arepopulated into the sequence recipe 4310. The sequence recipe 4310 thenpresents the sequence manager 4315 with a sequence of commands and thesequence manager 4315 assigns resources and causes the command sequenceto execute. The API may include a set of commands as described below.Each command generally includes a command name followed by commandarguments. In the commands of the disclosed embodiments the terms actor,resource, and robot refer to any device capable of performing anoperation.

A command for picking material from a specified material source locationusing a specified robot location may be called a PickFrom command andmay have the following format.

PickFrom(IRobot robot, int robotLocation, IMaterialHoldermaterialSource, int sourceLocation)where:

-   -   robot specifies the primary actor for the pick operation;    -   robotLocation specifies the actor index, usually the tip to be        used for the pick operation;    -   materialSource specifies the device that currently holds the        material; and    -   sourceLocation specifies the index into the device the material        resides in.

A command for placing material to a specified material destinationlocation using a specified robot location may be called a PlaceTocommand and may have the following format.

PlaceTo(IRobot robot, int robotLocation, IMaterialHoldermaterialDestination, int destinationLocation)where

-   -   robot specifies the primary actor(robot) for the place        operation;    -   robotLocation specifies the actor index, usually the tip the        material resides in;    -   materialDestination specifies the destination object; and    -   destinationLocation specifies the index into the destination        object.

A command for executing part of a PickFrom operation to a configuredpoint may be called PickPrep command. A PickPrep command may generallybe used to move a robot close to a specified material source to increasetool throughput. The operation may stop at a configured point unless aPickFrom command is sent prior to robot deceleration.

The PickPrep command may have the following form.

PickPrep(IRobot robot, int robotLocation, IMaterialHoldermaterialSource, int sourceLocation)where

-   -   robot specifies the primary actor for the pick operation;    -   robotLocation specifies the actor index, usually the tip to be        used for the pick operation;    -   materialSource specifies the device that currently holds the        material; and    -   sourceLocation specifies the index into the device the material        resides in.

A command that executes part of a PlaceTo operation to a configuredpoint may be called a PlacePrep command. A PlacePrep command maygenerally be used to move a robot close to a specified material sourceto increase tool throughput. The operation may stop at the configuredpoint unless a PlaceTo command is sent prior to robot deceleration.

The PlacePrep command may have the following form.

PlacePrep(IRobot robot, int robotLocation, IMaterialHoldermaterialDestination, int destinationLocation)where

-   -   robot specifies the primary actor(robot) for the place        operation;    -   robotLocation specifies the actor index, usually the tip the        material resides in;    -   materialDestination specifies the destination object; and    -   destinationLocation specifies the index into the destination        object.

A command that moves a substrate from a material source location to adestination location using a specified robot location may be called aMoveFromTo command and may have the following form.

MoveFromTo(IRobot robot, int robotLocation, IMaterialHoldermaterialSource, in sourceLocation IMaterialHolder materialDestination,int destinationLocation)where

-   -   robot specifies the primary actor to be used for the operation;    -   robotLocation specifies the actor index usually tip to be used        for operation;    -   materialSource specifies the object that currently holds the        material;    -   sourceLocation specifies the index into the object the material        resides in;    -   materialDestination specifies the destination object; and    -   DestinationLocation specifies the index into the destination        object.

A command that maps a specified resource using a specified mappingdevice may be referred to as a MapResource command. Mapping a resourcemay include determining if the resource is holding or supporting anyitems and may also include determining the location of the items beingheld or supported. The MapResource command may also update a record ofthe state of locations in the specified resource to an appropriatevalue, for example, occupied, unoccupied, etc.

The MapResource command may have the following form.

MapResource(IMapper mapper, IMaterialHolder resource)where

-   -   mapper identifies a device capable of mapping the specified        resource; and    -   resource identifies a device requiring mapping.

A command for initializing a specified resource to a ready condition maybe referred to as an InitializeResource command. For example; if theresource is a robot the InitializeResource command will cause the robotto move to a known position, or home and then to move to a safeposition. This command may also reset a locking mechanism of theresource in the event that the mechanism has been enabled.

The InitializeResource command may have the following form.

InitializeResource(IWorkcellObject resource)where resource specifies a resource to initialize.

A command for initializing resources based on a strategy or a recipe mayalso be referred to as an InitializeResources command. In the event thata strategy or recipe is not specified, a standard or default recipecould be to initialize robots first and then attached modules.

The InitializeResources command that utilizes a strategy may have theform:

InitializeResources(recipe)

where recipe specifies an initialization strategy.

It can be seen that the disclosed embodiments provide an API that allowsthe use of a general command to perform an operation with specificarguments to identify particular components, locations, and otherparameters for performing the operation. Thus, the disclosed embodimentsdescribe a networked control system that has the advantages of bothcentralized and distributed controls, that is flexible and scalable,that provides model based control, synchronizes component operations,and provides protocol extensions specifically for a system of thisarchitecture. The control system also provides distributed event captureand an application program interface. In addition, the system includes awireless communication capability, accommodates human presence in acomponent workspace, provides a high level of system integrity, providesfor power losses and circumstances that require an immediate stop, andprovides a warm-up capability to eliminate positional errors due to arobot's sitting idle.

What is claimed is:
 1. A method for controlling an axis of a controlsystem comprising: calculating an operating parameter value defining aforce value of an end effector of an axis in a first mode of axisoperation that is different than a corresponding force value of the endeffector in a second mode of axis operation; generating a motion profilefor an individual joint of the axis such that a motion profile for theend effector does not exceed the force value of the end effector in thefirst mode of axis operation.
 2. The method of claim 1, wherein theoperating parameter value is a maximum velocity.
 3. The method of claim1, wherein the operating parameter value is a maximum torque.
 4. Amethod for controlling an axis comprising: calculating, with acontroller, a velocity and a torque for a position of the axis;calculating, with the controller, a predetermined first maximum timeperiod during which an axis velocity may exceed the calculated velocity;calculating, with the controller, a predetermined second maximum timeperiod during which an axis torque may exceed the calculated torque;disabling, with the controller, the axis if one or more of the first andsecond maximum time period is exceeded.
 5. The method of claim 4,comprising disabling the axis if the calculated velocity exceeds apredetermined maximum velocity.
 6. The method of claim 5, comprisingdisabling the axis if the calculated torque exceeds a predeterminedmaximum torque.
 7. The method of claim 4, comprising disabling the axisupon failure to receive a periodic communication from the axis.
 8. Themethod of claim 4, comprising disabling the axis upon failure to receivea periodic communication from an axis controller.
 9. A method ofbringing an axis to a controlled stop comprising: determining if powerhas been lost to a system including the axis; setting a predeterminedtime period applying a mode of operation of the axis and applying atrajectory to the axis that brings the axis to a zero velocity withinthe predetermined time period where motion of the axis along thetrajectory is coordinated with motion of another axis; and removingpower from the axis at an end of the predetermined time period.
 10. Themethod of claim 9, wherein the predetermined time period is determinedby calculating a time remaining before power is lost to the axis.
 11. Amethod of verifying the integrity of data transmitted over a controlsystem network comprising: storing operating parameters at a node on thenetwork; and verifying that commands received through the network do notcause operations of the node that exceed the operating parameters. 12.The method of claim 11, comprising disabling the node if the commandscause operations of the node to exceed the operating parameters
 13. Themethod of claim 12, wherein the operating parameters include a maximumaxis velocity.
 14. The method of claim 11, wherein the operatingparameters include an axis velocity error.
 15. The method of claim 11,wherein the operating parameters include a time during which a maximumvelocity may be exceeded.
 16. A method of verifying the integrity of acontrol system network comprising: issuing a periodic message; anddisabling one or more nodes of the control system network if the messageis not received within a time period.
 17. The method of claim 16,wherein the message is a position velocity time message frame.
 18. Themethod of claim 16, wherein the message is issued by a networkcontroller and the one or more nodes are disabled if a first node of theone or more nodes does not receive the message.
 19. The method of claim16, wherein the message is issued by the one or more nodes and the oneor more nodes are disabled if a network controller does not receive themessage.
 20. The method of claim 16, comprising removing power fromselected ones of the one or more nodes if the message is not receivedwithin a time period.
 21. A method of maintaining the integrity of acontrol system network comprising: assigning nodes of the network intozones such that motion in a first zone is isolated from motion in zonesother than the first zone; and controlling the zones so that events ofthe first zone do not effect the operation of zones other than the firstzone.
 22. The method of claim 21, comprising disabling the first zoneand routing work designated for the first zone to a zone other than thefirst zone.